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Kurzweil-Henstock Integral in Riesz spaces - Bentham Science

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<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong><br />

<strong>in</strong> <strong>Riesz</strong> <strong>spaces</strong><br />

Antonio Boccuto<br />

Beloslav Riean<br />

Marta Vrábelová<br />

2009


CONTENTS<br />

Foreword i<br />

Preface ii<br />

Contributors iv<br />

1. Elementary Introduction to <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> 1<br />

1.1 Introduction 1<br />

1.2 Def<strong>in</strong>ition of <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral 3<br />

1.3 Basic theorems 6<br />

1.4 Cont<strong>in</strong>uity of the <strong>in</strong>tegral 9<br />

1.5 Fundamental theorem of calculus 10<br />

1.6 Improper <strong>in</strong>tegrals 12<br />

1.7 Absolute <strong>in</strong>tegrability 14<br />

1.8 Convergence theorems 18<br />

1.9 Unbounded <strong>in</strong>tervals 23<br />

2 Elementary Theory of <strong>Riesz</strong> Spaces 25<br />

2.1 Lattice ordered groups 25<br />

2.2 Weak σ-distributivity 29<br />

2.3 <strong>Riesz</strong> <strong>spaces</strong> 36<br />

3 <strong>Kurzweil</strong> - <strong>Henstock</strong> <strong>Integral</strong> with Values <strong>in</strong> <strong>Riesz</strong> Spaces 42<br />

3.1 Def<strong>in</strong>ition and elementary properties 42<br />

3.2 Uniform convergence theorem 48<br />

3.3 <strong>Kurzweil</strong> - Stieltjes <strong>in</strong>tegral 49<br />

4 Double <strong>Integral</strong>s 52<br />

4.1 Def<strong>in</strong>ition of the double <strong>in</strong>tegral 52<br />

4.2 Double <strong>in</strong>tegral of cont<strong>in</strong>uous functions 56<br />

4.3 Compound partitions 59<br />

4.4 Fub<strong>in</strong>i’s theorem 60<br />

5 <strong>Kurzweil</strong> - <strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> Topological Spaces 62<br />

5.1 Elementary properties 62<br />

5.2 Monotone convergence theorem 66<br />

6 Convergence Theorems 71<br />

6.1 Elementary properties 71<br />

6.2 General convergence theorems 74<br />

6.3 <strong>Henstock</strong> lemma 76<br />

6.4 Levi’s theorem 77<br />

6.5 Lebesgue’s theorem 80


7 Improper <strong>Integral</strong> 84<br />

7.1 Real valued case 84<br />

7.2 Vector valued case 99<br />

8 Choquet and Šipoš <strong>Integral</strong>s 111<br />

8.1 Symmetric <strong>Integral</strong> 111<br />

8.2 Asymmetric <strong>in</strong>tegral 126<br />

8.3 Applications 127<br />

9 (SL)-<strong>Integral</strong> 134<br />

9.1 Ma<strong>in</strong> properties <strong>in</strong> the real and <strong>Riesz</strong> space context 134<br />

9.2 Convergence theorems 158<br />

10 Pettis-Type Approach 166<br />

10.1 Banach space valued case 166<br />

10.2 <strong>Riesz</strong> space valued case 172<br />

11 Applications <strong>in</strong> Multivalued Logic 178<br />

11.1 MV-algebras 178<br />

11.2 Group-valued measures 181<br />

11.3 Intuitionistic fuzzy sets 184<br />

12 Applications <strong>in</strong> Probability Theory 187<br />

12.1 Independence 187<br />

12.2 Conditional probability 191<br />

12.3 Probability theory on IF-events 194<br />

13 Integration <strong>in</strong> Metric Semigroups 198<br />

13.1 Elementary properties 198<br />

13.2 Convergence theorems 208<br />

References 213<br />

Subject Index 224


FOREWORD<br />

In 1956 Jaroslav <strong>Kurzweil</strong> was <strong>in</strong>volved <strong>in</strong> special phenomena occurr<strong>in</strong>g <strong>in</strong><br />

ord<strong>in</strong>ary differential equations with fast oscillat<strong>in</strong>g entries which have not been<br />

justified by theories and approaches known at those times. For expla<strong>in</strong><strong>in</strong>g the<br />

observed results he constructed a tool, which rem<strong>in</strong>ded <strong>in</strong> some aspects strongly the<br />

way how the Perron <strong>in</strong>tegral us<strong>in</strong>g m<strong>in</strong>or and major functions was constructed. The<br />

story ended by a success and the tool became an <strong>in</strong>dependent, self-conta<strong>in</strong>ed object,<br />

the generalized Perron <strong>in</strong>tegral.<br />

S<strong>in</strong>ce the generalized Perron <strong>in</strong>tegral occurred to be very <strong>in</strong>terest<strong>in</strong>g and, due to the<br />

need of research, it was described via <strong>in</strong>tegral sums of Riemann type, Jaroslav<br />

<strong>Kurzweil</strong> described it <strong>in</strong> detail <strong>in</strong> his very first paper [163] on the topic and used it<br />

<strong>in</strong> a series of subsequent writ<strong>in</strong>gs on ord<strong>in</strong>ary differential equations. Only a<br />

restricted number of people knew at this times about the existence of a newly<br />

def<strong>in</strong>ed <strong>in</strong>tegral. There is no reason to be surprised by this fact, look<strong>in</strong>g at the title<br />

of [163] nobody can expect deep <strong>in</strong>terest of mathematicians <strong>in</strong>volved <strong>in</strong> <strong>in</strong>tegration<br />

theory <strong>in</strong> this paper.<br />

In the same time Ralph <strong>Henstock</strong> worked on variational approaches to <strong>in</strong>tegrals, no<br />

exist<strong>in</strong>g connection to <strong>Kurzweil</strong> <strong>in</strong> those days. For the first time the possible<br />

relation is mentioned cautiously <strong>in</strong> <strong>Henstock</strong>’s booklet [153].<br />

It was discovered early <strong>in</strong> the sixties that <strong>in</strong> the case of real valued functions both<br />

approaches (that of <strong>Henstock</strong> and of <strong>Kurzweil</strong>) are equivalent and, of course, the<br />

def<strong>in</strong>ition of the very general non-absolutely convergent <strong>in</strong>tegral based on<br />

Riemann-type <strong>in</strong>tegral sums came to the foreground.<br />

The dist<strong>in</strong>ctive <strong>in</strong>dividual life of an <strong>in</strong>tegration theory, the <strong>Kurzweil</strong>-<strong>Henstock</strong><br />

<strong>in</strong>tegral, started <strong>in</strong> the second half of seventies. With all of its advantages and<br />

drawbacks com<strong>in</strong>g to general awareness.<br />

One of the <strong>in</strong>terest<strong>in</strong>g po<strong>in</strong>ts of <strong>in</strong>tegration theories is the problem when functions<br />

with values <strong>in</strong> general <strong>spaces</strong> have to be <strong>in</strong>tegrated. This problem is of <strong>in</strong>terests<br />

especially <strong>in</strong> the case of <strong>in</strong>f<strong>in</strong>ite dimensional <strong>spaces</strong> equipped with some topology,<br />

the models are e. g. the Bochner, Dunford and Pettis <strong>in</strong>tegrals of Banach spacevalued<br />

functions based on the Lebesgue approach.<br />

The book of A. Boccuto, B. Riean and M. Vrábelová is oriented <strong>in</strong> this direction.<br />

The functions which are <strong>in</strong>tegrated have values <strong>in</strong> <strong>Riesz</strong> <strong>spaces</strong> <strong>in</strong> general. The<br />

comb<strong>in</strong>ation of techniques used <strong>in</strong> <strong>Riesz</strong> <strong>spaces</strong> with the more or less algebraic<br />

approach which is <strong>in</strong> charge for <strong>in</strong>tegrals based on Riemann type <strong>in</strong>tegral sums<br />

makes the presentation <strong>in</strong>terest<strong>in</strong>g and <strong>in</strong>spirative for further research. Besides their<br />

own research the authors present also short <strong>in</strong>sights <strong>in</strong>to applications and less<br />

known theories. All this makes the value of the present book, which should reach<br />

the reader <strong>in</strong> an unorthodox form. I am sure we are fac<strong>in</strong>g an <strong>in</strong>spirative text, with<br />

many new <strong>in</strong>formation and maybe also a nice reference text <strong>in</strong> various fields of<br />

analysis.<br />

tefan Schwabik, Prague<br />

i


ii<br />

PREFACE<br />

<strong>Kurzweil</strong> and <strong>Henstock</strong>’s idea to construct a new type of <strong>in</strong>tegral turned out to<br />

be both surpris<strong>in</strong>gly successful and extremely useful, not only from the didactic but<br />

also from the scientific po<strong>in</strong>t of view. It has very promis<strong>in</strong>g applications, for<br />

example <strong>in</strong> differential equations and surface <strong>in</strong>tegrals. <strong>Riesz</strong> <strong>spaces</strong>, on the other<br />

hand, offer a very important tool <strong>in</strong> modern mathematics and have many practical<br />

applications, for example <strong>in</strong> economics. Recall that the em<strong>in</strong>ent mathematician and<br />

Nobel Prize L. V. Kantorovich was the founder of the theory of <strong>Riesz</strong> <strong>spaces</strong>. This<br />

monograph is concerned with both the theory of the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral<br />

and the basic facts on <strong>Riesz</strong> <strong>spaces</strong>.<br />

Another important application of this theory was discovered recently. In 2002 D.<br />

Kahneman received the Nobel Prize <strong>in</strong> Economics. While he was look<strong>in</strong>g for a<br />

theoretical basis on his economical theory, he found an appropriate mathematical<br />

model: the so-called ipo <strong>in</strong>tegral, one of the topics we present <strong>in</strong> this<br />

monograph.<br />

It is well-known that <strong>in</strong>tegration theory with values <strong>in</strong> ordered <strong>spaces</strong> cannot be<br />

reduced to the analogous theory for locally convex <strong>spaces</strong>. This fact justifies the<br />

ma<strong>in</strong> goal of this book: to <strong>in</strong>vestigate and develop a measure and <strong>in</strong>tegration theory<br />

of the <strong>Kurzweil</strong>-<strong>Henstock</strong> type for functions with values <strong>in</strong> ordered <strong>spaces</strong>.<br />

The first chapter offers to the reader a self-conta<strong>in</strong>ed treatment of the realvalued<br />

theory of the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral. Namely, the extremely simple<br />

def<strong>in</strong>ition enables us to use a very concise and effective theory.<br />

The follow<strong>in</strong>g chapter on <strong>Riesz</strong> <strong>spaces</strong> should also be accessible to a large class<br />

of readers. We not only mention slightly more general structures such as lattice<br />

ordered groups, but also some basic facts about MV-algebras: these are important<br />

for multivalued logic. The general theory of the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral <strong>in</strong><br />

<strong>Riesz</strong> <strong>spaces</strong> is presented <strong>in</strong> the third chapter. As discovered by J. D. M. Wright<br />

and D. Freml<strong>in</strong>, there exists a sufficient and necessary condition for the possibility<br />

to extend <strong>Riesz</strong> space-valued Daniell <strong>in</strong>tegrals from the set of simple functions to<br />

the set of <strong>in</strong>tegrable functions, or a <strong>Riesz</strong> space-valued measure from an algebra to<br />

the generated -algebra. This condition, which is called weak -distributivity,<br />

holds <strong>in</strong> any probability MV-algebra.<br />

Chapters 4 - 6 conta<strong>in</strong> new and, <strong>in</strong> our op<strong>in</strong>ion, important results on<br />

convergence theorems and multiple <strong>in</strong>tegrals. These chapters also conta<strong>in</strong> a<br />

systematic exposition of the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral theory for functions<br />

def<strong>in</strong>ed on abstract topological <strong>spaces</strong>. Recall that most papers on the <strong>Kurzweil</strong>-<br />

<strong>Henstock</strong> <strong>in</strong>tegral use as a doma<strong>in</strong> only Euclidean <strong>spaces</strong>.<br />

Some more special topics are treated <strong>in</strong> chapters 7 - 10 and 13, namely improper<br />

<strong>in</strong>tegrals, SL-<strong>in</strong>tegrals, the Pettis and Choquet approach, and <strong>in</strong>tegration <strong>in</strong> metric<br />

semigroups. The Choquet <strong>in</strong>tegral (or its ipo symmetric variant) is of particular<br />

importance <strong>in</strong> non-additive measures.


In chapters 11 and 12 we are concerned with some applications to probability<br />

theory. In particular, it is important to observe that a probability theory on the socalled<br />

<strong>in</strong>tuitionistic fuzzy sets can be constructed by consider<strong>in</strong>g them as embedded<br />

<strong>in</strong> an appropriate MV-algebra.<br />

As we mentioned before, the aim of this monograph is two-fold. First, it can be<br />

understood as an <strong>in</strong>troductory textbook to the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral as well<br />

as to some algebraic structures (<strong>Riesz</strong> <strong>spaces</strong>, l-groups, MV-algebras) which are<br />

important from the viewpo<strong>in</strong>t of applications to <strong>in</strong>tegration and probability theory.<br />

Second, it offers some possibilities of further developments <strong>in</strong>clud<strong>in</strong>g important<br />

open problems <strong>in</strong> this attractive area, with a glimpse of the diversity of directions <strong>in</strong><br />

which the current research is mov<strong>in</strong>g.<br />

The first author wants to dedicate this book to the lov<strong>in</strong>g memory of his mother<br />

Teresa who passed away on August 2nd, 2004, while Antonio was <strong>in</strong> Slovakia for<br />

cooperat<strong>in</strong>g with Prof. Riean. She always helped him, not only <strong>in</strong> overcom<strong>in</strong>g<br />

many difficulties <strong>in</strong> his personal life, but she also encouraged him to leave Italy <strong>in</strong><br />

order to broaden his fields of <strong>in</strong>terest and to enrich his personal experiences. That is<br />

why he decided to participate <strong>in</strong> the W<strong>in</strong>ter School on Measure Theory <strong>in</strong><br />

Liptovsk Ján <strong>in</strong> 1993, which marked the beg<strong>in</strong>n<strong>in</strong>g of a fruitful cooperation with<br />

his Slovak colleagues and friendship with marvellous people from Slovakia. The<br />

present book is the outcome of this wonderful cooperation and friendship which,<br />

hopefully, will cont<strong>in</strong>ue for still many years to come.<br />

The third author wants to thank Antonio Boccuto and Beloslav Riean for the<br />

nice teamwork and friendship and Prof. Riean for the scientific upbr<strong>in</strong>g<strong>in</strong>g.<br />

We would like to thank Prof. tefan Schwabik for writ<strong>in</strong>g the foreword and<br />

<strong>Bentham</strong> <strong>Science</strong> Publishers, particularly Manager Bushra Siddiqui, for their<br />

support and efforts.<br />

iii


iv<br />

KURZWEIL-HENSTOCK INTEGRAL<br />

IN RIESZ SPACES<br />

Antonio Boccuto, Beloslav Riean, Marta Vrábelová<br />

Abstract: This monograph is concerned with both the theory of the <strong>Kurzweil</strong>-<br />

<strong>Henstock</strong> <strong>in</strong>tegral and the basic facts on <strong>Riesz</strong> <strong>spaces</strong>. Moreover even the so-called<br />

ipo <strong>in</strong>tegral, which has several applications <strong>in</strong> economy,is illustrated. The aim of<br />

this book is two-fold. First, it can be understood as an <strong>in</strong>troductory textbook to the<br />

<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral as well as to some algebraic structures which are<br />

important from the viewpo<strong>in</strong>t of applications to <strong>in</strong>tegration and probability theory.<br />

Second, it discusses some possibilities of further developments <strong>in</strong>clud<strong>in</strong>g recent<br />

results and open problems.<br />

CONTRIBUTORS<br />

Antonio Boccuto, Doc., Ph.D.<br />

Assistant Professor, Dipartimento di Matematica e Informatica, via Vanvitelli, 1<br />

I-06123 Perugia, Italy Email: boccuto@yahoo.it<br />

Beloslav Riean, Prof. RNDr., DrSc.<br />

Professor, Matej Bel University, Tajovského 40, SK-97401 Banská Bystrica,<br />

Slovakia,<br />

and Mathematical Institute, Slovak Academy of <strong>Science</strong>, tefánikova 49, SK-<br />

81473 Bratislava, Slovakia Email: riecan@fpv.umb.sk<br />

Marta Vrábelová, Doc. RNDr., CSc.<br />

Professor, Constant<strong>in</strong>e the Philosopher University, Tr. A. Hl<strong>in</strong>ku 1, SK-94974<br />

Nitra, Slovakia Email: mvrabelova@ukf.sk<br />

Address correspondence to<br />

Antonio Boccuto, Dipartimento di Matematica e Informatica, via Vanvitelli, 1 I-<br />

06123 Perugia, Italy, fax +39 075 5855024 Email: boccuto@yahoo.it


<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 1-24 1<br />

1 Elementary Introduction to <strong>Kurzweil</strong>-<strong>Henstock</strong><br />

<strong>Integral</strong><br />

Abstract<br />

In this chapter we <strong>in</strong>troduce the theory of the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral for real-valued functions, def<strong>in</strong>ed on a<br />

bounded <strong>in</strong>terval of the real l<strong>in</strong>e.<br />

The ma<strong>in</strong> properties are illustrated, the Fundamental Theorem of Calculus and some convergence theorems are proved;<br />

moreover some examples and exercises are given.<br />

1.1 Introduction<br />

In this section we <strong>in</strong>troduce the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral (or the gauge <strong>in</strong>tegral or the generalized<br />

Riemann <strong>in</strong>tegral) for real-valued functions f def<strong>in</strong>ed on a bounded <strong>in</strong>terval[ ab , ] ⊂ R , only <strong>in</strong><br />

Subsection 1.9 the <strong>in</strong>terval [ ab , ] is taken unbounded.<br />

The <strong>in</strong>tegral theory, which we are speak<strong>in</strong>g about, was, <strong>in</strong>dependently, <strong>in</strong>troduced by Ralph<br />

<strong>Henstock</strong> (1955) and Jaroslav <strong>Kurzweil</strong> (1957). This <strong>in</strong>tegral is simpler than the Lebesgue <strong>in</strong>tegral<br />

and as strong as the Denjoy-Perron <strong>in</strong>tegral. The def<strong>in</strong>ition is similar to the def<strong>in</strong>ition of the<br />

Riemann <strong>in</strong>tegral.<br />

This chapter does not fetch new results. Its aim is that the reader became familiar with the<br />

<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral theory. Our <strong>in</strong>tention is especially to po<strong>in</strong>t out some differences<br />

between the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral and the Riemann <strong>in</strong>tegral. The proofs and the solutions are<br />

given <strong>in</strong> details and the section is readable for a reader with an elementary knowledge of the<br />

calculus. For a deeper study of this theory there are a few <strong>in</strong>terest<strong>in</strong>g books. We mention, for<br />

example, the books written by Robert McLeod [188], Lee Peng Yee and Rudolf Výborný [170], and<br />

Charles Swartz [254].<br />

A division of a compact <strong>in</strong>terval [ ab , ] is a f<strong>in</strong>ite, ordered sequence of po<strong>in</strong>ts<br />

a= a0 < a1 < …< an= b.<br />

By choos<strong>in</strong>g a number ti∈ [ ai−1, ai]<br />

for i = 12 , , …, n a partition P of [ ab , ] is def<strong>in</strong>ed,<br />

P = {([ ai−1, ai] , ti) : i = 1, 2 , …, n}<br />

.<br />

If δ > 0,<br />

then a partition P with<br />

ti − δ < ai−1≤ti ≤ ai < ti<br />

+ δ<br />

for i = 12 , , …, n is called a δ -f<strong>in</strong>e partition of [ ab , ] .<br />

Lets suppose that f is a bounded real-valued function def<strong>in</strong>ed on[ ab , ] . A Riemann sum for the<br />

P = {([ a , a ] , t ) : i = 1, 2 , …, n}<br />

of the <strong>in</strong>terval [ ab , ] is the number<br />

function f and the partition i−1 n<br />

i i<br />

∑ ∑<br />

f = f( ti)( ai − ai−1) .<br />

P i=<br />

1<br />

Generally, a partition P of [ ab , ] is a set of the type<br />

P = {( Ei, ti) : i = 1, 2 , …, n}<br />

,<br />

where i E are non-overlapp<strong>in</strong>g, closed <strong>in</strong>tervals, n<br />

ti∈ Ei<br />

for i = 12 , , …, n and U i= 1 Ei = [ a, b]<br />

. The<br />

Riemann sum is the quantity<br />

n<br />

∑ ∑<br />

f = f( t ) |E | ,<br />

P i=<br />

1<br />

i i<br />

where |E i | is the length of the <strong>in</strong>terval E i , i = 1,<br />

…, n.<br />

Antonio Boccuto / Beloslav Riečan / Marta Vrábelová<br />

All rights reserved - © 2009 <strong>Bentham</strong> <strong>Science</strong> Publishers Ltd.


2 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riečan, M. Vrábelová<br />

Def<strong>in</strong>ition 1.1 A function f : [ a, b]<br />

→R is Riemann <strong>in</strong>tegrable if there is a real number I such<br />

that for every ε > 0 there is δ > 0 such that<br />

| f − I| < ε<br />

∑<br />

P<br />

for every δ -f<strong>in</strong>e partition P .<br />

In this case, the number I is called the Riemann <strong>in</strong>tegral of f on [ ab , ] and its standard<br />

b<br />

notation is f ( xdx. )<br />

∫<br />

a<br />

The def<strong>in</strong>ition fails for an unbounded function. If f is a Riemann <strong>in</strong>tegrable function then f is<br />

bounded.<br />

Suppose f( x) ≥ 0 for x ∈ [ ab , ] . Then the Riemann sum is an approximation to the area of the<br />

region under the graph of f . To have a good approximation, the width of the <strong>in</strong>terval [ ai− 1,<br />

ai]<br />

must<br />

be small whenever the graph of f is steep, but it can be wider where the graph of f is more<br />

horizontal.<br />

It is a good idea to take the po<strong>in</strong>ts t1, t2, …t , n from [ ab , ] and with respect to the behavior of f to<br />

choose numbers δ ( ti<br />

) > 0 and <strong>in</strong>tervals [ ai− 1,<br />

ai]<br />

, i 12…<br />

n = , , , , such that f ( ti)( ai − ai−1) is a good<br />

approximation to the area of the strip under the graph between the l<strong>in</strong>es x = ai−1 and x = ai<br />

for<br />

i = 12 , , …, n.<br />

+<br />

In other words, the function δ : [ ab , ] →R is taken <strong>in</strong>stead of the number δ > 0 . Then a δ -f<strong>in</strong>e<br />

partition P of the <strong>in</strong>terval [ ab , ] is the set<br />

P = {([ ai−1, ai], ti): ti∈[ ai−1, ai] ⊂( ti − δ ( ti), ti + δ ( ti)),<br />

i = 1, 2, … , n}<br />

.<br />

A construction of the function δ will be showed <strong>in</strong> the follow<strong>in</strong>g example.<br />

1<br />

1<br />

Example 1.2 Let f ( m)<br />

= m for every m∈N and f( x ) = 0 for x∈ [0, 1]\{ m : m∈<br />

N } . We will<br />

+<br />

def<strong>in</strong>e a function δ : [0, 1] →R such that<br />

∑ ∫<br />

P<br />

0<br />

for every δ -f<strong>in</strong>e partition P = ai−1, ai , ti<br />

1<br />

f − f( x) dx < ε<br />

{([ ] ),<br />

i = 1, 2, … , n}<br />

of [0, 1] .<br />

S<strong>in</strong>ce the area of the region under the graph of f is zero,<br />

1<br />

∫ f( x) dx= 0 and we need a function<br />

0<br />

δ such that f ε P < ∑ for any δ -f<strong>in</strong>e partition P of [0, 1] . The function δ , <strong>in</strong> general, cannot be a<br />

small constant. Indeed,<br />

n n<br />

∑ ∑<br />

f ( t )( a − a ) < 2 δ f ( t )<br />

i i i−1 i<br />

i= 1 i=<br />

1<br />

n<br />

and ∑ f ( t )<br />

i=<br />

1 i is not bounded on [0, 1] . The value f ( t i)<br />

is nonzero <strong>in</strong> the case ti= 1/<br />

m for some<br />

m∈N only if 1/ m is equal to at most two t i , namely ti− 1 and t i for some i. Hence, it is appropriate<br />

to take<br />

1<br />

2<br />

2 m<br />

⎛ ⎞ ε<br />

δ ⎜ ⎟=<br />

+<br />

⎝m⎠ m


Elementary Introduction to <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 3<br />

for m∈N and δ ( x)<br />

can be any positive number for x∈ [0, 1] ‚ {1 / m: m∈N}<br />

, say δ ( x)<br />

= 1.<br />

Put<br />

M = { m∈ N : ti= 1/ m, i= 1, 2 , …, n}<br />

. Then<br />

n<br />

∞ ε ε<br />

∑ f = ∑ f( ti)( ai −ai− 1) ≤ ∑ 2m<br />

< ε<br />

m+ 1 ∑ = . m<br />

P i= 1 m∈ M m2<br />

m=<br />

1 2<br />

The δ -f<strong>in</strong>e partition P that we have used <strong>in</strong> the previous example exists, for example<br />

P = {([0,1], 2 / 2)} .<br />

The compatibility theorem (or Cous<strong>in</strong>’s lemma) guarantees the existence of a δ -f<strong>in</strong>e partition<br />

+<br />

for every function δ : [ ab , ] → R .<br />

+<br />

Theorem 1.3 Let δ : [ ab , ] →R and a≤ c< d ≤ b.<br />

Then there exists a δ -f<strong>in</strong>e partition of [ cd , ] .<br />

Proof: By contradiction, suppose that there is no δ -f<strong>in</strong>e partition of [ cd , ] . Divide the <strong>in</strong>terval<br />

[ cd , ] <strong>in</strong>to the <strong>in</strong>tervals<br />

⎡ c+ d⎤ ⎡c+ d ⎤<br />

⎢<br />

c, , , d .<br />

⎣ 2 ⎥<br />

⎦<br />

⎢<br />

⎣ 2 ⎥<br />

⎦<br />

Then one of them has no δ -f<strong>in</strong>e partition. Denote that <strong>in</strong>terval by [ c1, d1]<br />

.<br />

The cont<strong>in</strong>uation by this manner creates a sequence of nested <strong>in</strong>tervals<br />

[ ] ( ) 2 n<br />

cn, dn , dn − cn = d − c / .<br />

∞<br />

Then there is one po<strong>in</strong>t e∈ I n= 1 [ cn, dn]<br />

. S<strong>in</strong>ce δ () e > 0,<br />

there is n0 ∈ N such that dn − cn < δ ( e)<br />

for<br />

every n> n0.<br />

Hence,<br />

P = {([ cn, dn] , e)} ( n> n0)<br />

is a δ -f<strong>in</strong>e partition of [ c , d ] , that is a contradiction.<br />

n n<br />

Exercise 1.4 Construct a δ -f<strong>in</strong>e partition P of [0, 1] when<br />

⎛ m ⎞ ε<br />

δ ⎜ ⎟=<br />

, m+<br />

2<br />

⎝m+ 1⎠ 2<br />

⎧ m−1m ⎫<br />

δ(<br />

x) = m<strong>in</strong>⎨x−<br />

, −x⎬<br />

⎩ m m+<br />

1 ⎭<br />

x∈ m−1m , ( m= 012 , , , …)<br />

and δ (1) = ε / 2.<br />

for ( )<br />

m m+<br />

1<br />

H<strong>in</strong>t. Take n for which n/ ( n+ 1) > 1− ε / 2.<br />

All po<strong>in</strong>ts m/ ( m+ 1) = t2m+ 1 ( m= 01 , , …, n)<br />

and 1 must be tags. Take bounds of <strong>in</strong>tervals such that<br />

ε<br />

a1 < ,<br />

4<br />

m ε m m ε<br />

− < a 2 2m < < a m 2m+ 1 < + + m+<br />

2<br />

m+ 1 2 m+ 1 m+<br />

1 2<br />

( m= 1, 2 , …, n)<br />

.<br />

Furthermore, put t2 = (( m− 1) / m+ m/ ( m+ 1)) / 2 ( m= 1, 2 , …, n)<br />

.<br />

m<br />

1.2 Def<strong>in</strong>ition of <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong><br />

Def<strong>in</strong>ition 1.5 A function f : [ a, b]<br />

→R is <strong>Kurzweil</strong>–<strong>Henstock</strong> <strong>in</strong>tegrable, if there is a real number<br />

+<br />

I such that for every ε > 0 there is a function δ : [ ab , ] →R such that<br />

| f − I| < ε<br />

∑<br />

P<br />

for every δ -f<strong>in</strong>e partition P of [ ab , ] .<br />

We will denote the <strong>Kurzweil</strong>–<strong>Henstock</strong> <strong>in</strong>tegral ( ( KH ) -<strong>in</strong>tegral) I of f on [ ab , ] by the<br />

symbol<br />

b<br />

( KH ) f ( xdx. )<br />

∫<br />

a


<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 25-41 25<br />

2 Elementary Theory of <strong>Riesz</strong> Spaces<br />

Abstract<br />

In this chapter we deal with the fundamental properties of lattice groups and <strong>Riesz</strong> <strong>spaces</strong>. We <strong>in</strong>troduce the concepts of<br />

order and (D)-convergence, weak -distributivity and Egorov property and prove some related results. We deal also<br />

with order bounded and order cont<strong>in</strong>uous l<strong>in</strong>ear functionals <strong>in</strong> the sett<strong>in</strong>g of <strong>Riesz</strong> <strong>spaces</strong>. F<strong>in</strong>ally we <strong>in</strong>troduce the<br />

Maeda-Ogasawara-Vulikh representation theorem.<br />

2.1 Lattice Ordered Groups<br />

Throughout this chapter, given a< b<br />

R , we will denote by [ ab , ] the closed <strong>in</strong>terval<br />

{ x R : a xb} and by ( ab , ) the open <strong>in</strong>terval { x R : a< x< b}.<br />

Def<strong>in</strong>ition 2.1 A partially ordered set R is a nonempty set endowed with a reflexive, transitive<br />

and antisymmetric relation, denoted by .<br />

Given a nonempty subset A R and an element s R,<br />

we say that s is the supremum of A if for<br />

every element a A we have a s,<br />

and moreover we get s c whenever c R and c b for all<br />

b A.<br />

Analogously, given j R,<br />

we say that j is the <strong>in</strong>fimum of A if for each a A we have<br />

a j,<br />

and for all d R,<br />

such that d b b A,<br />

we get j d . In this case, we write s = sup A<br />

and j = <strong>in</strong>f A respectively.<br />

If is any nonempty set and ( x) is a family of elements <strong>in</strong> R , we denote also by x and<br />

x , or sup x<br />

and <strong>in</strong>f x,<br />

the quantities sup{ x : } and <strong>in</strong>f { x : }<br />

respectively, provided that they exist <strong>in</strong> R .<br />

A partially ordered set R is said to be a lattice if for every two elements a , b R there exist <strong>in</strong> R<br />

the supremum s:= a b ( = sup {a, b} ) and the <strong>in</strong>fimum j:= a b ( = <strong>in</strong>f{ ab , }) . In a partially<br />

ordered set R , we say that a nonempty subset A R is bounded from above, if there exists x A<br />

such that a x,<br />

a A;<br />

bounded from below, if there exists y A such that a y,<br />

a A;<br />

bounded, if it is bounded both from above and from below.<br />

A lattice R is said to be Dedek<strong>in</strong>d complete if every nonempty subset of R , bounded from above<br />

(with respect to the relation ), admits supremum <strong>in</strong> R , and every nonempty subset of R , bounded<br />

from below, admits <strong>in</strong>fimum <strong>in</strong> R . A Dedek<strong>in</strong>d complete lattice R is said to be super Dedek<strong>in</strong>d<br />

complete if, for any nonempty set A R,<br />

bounded from above, there exists a countable subset<br />

<br />

A A,<br />

such that sup A= sup A , and for every nonempty set B R,<br />

bounded from below, there<br />

<br />

exists a countable subset B B,<br />

such that <strong>in</strong>f B= <strong>in</strong>f B .<br />

An element a of a lattice R is said to be positive if a 0 . Two positive elements ab , R are<br />

said to be disjo<strong>in</strong>t or orthogonal if a b=<br />

0 . A nonempty set A R is called a disjo<strong>in</strong>t system if<br />

every element a A is positive and a b=<br />

0 ab , A.<br />

Given any two elements a , b R,<br />

we<br />

say that a< b or b> a if a b and a b.<br />

A unit of R is an element a such that a > 0 .<br />

A lattice R is said to be laterally complete if every disjo<strong>in</strong>t system A R has a supremum <strong>in</strong><br />

R . We say that R is universally complete if it is both Dedek<strong>in</strong>d and laterally complete.<br />

Def<strong>in</strong>ition 2.2 Let R be a lattice. A nonempty set C R is said to be directed upwards<br />

[downwards ] if for every pair ab , C there exists c C such that c a,<br />

c b [c a,<br />

c b]<br />

.<br />

Antonio Boccuto / Beloslav Riean / Marta Vrábelová<br />

All rights reserved - © 2009 <strong>Bentham</strong> <strong>Science</strong> Publishers Ltd.


26 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riean, M. Vrábelová<br />

Def<strong>in</strong>ition 2.3 An Abelian partially ordered group ( R,+, ) is called a lattice ordered group (or<br />

briefly an l -group) if it is a lattice and the follow<strong>in</strong>g implication holds:<br />

<br />

[ ab] [ a+ c b+ c] abc , , R.<br />

(2.1)<br />

The follow<strong>in</strong>g properties hold <strong>in</strong> any l -group R (see [14], pp. 292-295).<br />

Proposition 2.4 (Distributive laws) For every abxy , , , R,<br />

we have:<br />

a+ ( x y) = ( a+ x) ( a+ y)<br />

,<br />

a+ ( x y) = ( a+ x) ( a+ y)<br />

,<br />

and, more generally, for each family ( x) of elements of R ,<br />

<br />

<br />

( )<br />

<br />

a+ x =<br />

a+ x ,<br />

<br />

<br />

<br />

<br />

<br />

( )<br />

<br />

a+ x =<br />

a+ x ,<br />

<br />

<br />

<br />

<strong>in</strong> the sense that the left member exists <strong>in</strong> R if and only if the right member exists <strong>in</strong> R too, and <strong>in</strong><br />

this case the two <strong>in</strong>volved quantities co<strong>in</strong>cide.<br />

Proposition 2.5 In any l -group R , we have<br />

a( a b) + b= ba a, b R.<br />

+ + <br />

Def<strong>in</strong>ition 2.6 For every element r of an l -group R , set r = r<br />

0 , r = ( r) 0;<br />

r and r are<br />

called the positive and negative part of r respectively. Moreover, set r = r( r)<br />

; r is called the<br />

absolute value of R .<br />

Proposition 2.7 For each element r of an l -group, we have:<br />

+ + <br />

r = r r ; r = r + r .<br />

Moreover, r 0 and r = 0 if and only if r = 0 .<br />

Def<strong>in</strong>ition 2.8 Given a R and n N , we denote by na the element a+ …+ a ( n times).<br />

The follow<strong>in</strong>g results hold <strong>in</strong> any l -group (see [14], p. 296):<br />

i) na = n a n N , aR; ii) ( ac) ( b c) + ( ac) ( b c) = ( ab) ( ab) a, b, cR<br />

;<br />

iii) a+ b a + b a, b R.<br />

Def<strong>in</strong>ition 2.9 An l -group R is said to be Archimedean if, for every choice of ab , R,<br />

with<br />

na b nN , we have: a 0 .


Elementary Theory of <strong>Riesz</strong> Spaces <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 27<br />

Proposition 2.10 Every Dedek<strong>in</strong>d complete l -group R is Archimedean.<br />

Proof: (See also [14], p. 291) Let ab , R,<br />

with na b nN . By Dedek<strong>in</strong>d completeness of R ,<br />

the element c na does exist <strong>in</strong> R . Thus, we get:<br />

:= nN<br />

Hence, we obta<strong>in</strong>: a 0 .<br />

<br />

c + a = ( n + 1) a na = c.<br />

nN nN<br />

Remark 2.11 In this book, we will <strong>in</strong>vestigate ma<strong>in</strong>ly Dedek<strong>in</strong>d complete l -groups. We note that<br />

the def<strong>in</strong>ition of l -group can be given without requir<strong>in</strong>g commutativity a priori: this, substantially,<br />

is not a restriction for our purposes. Indeed, by virtue of the Iwasawa theorem (see [14], p. 317),<br />

every Dedek<strong>in</strong>d complete partially ordered group ( R,+, ) which is a lattice and satisfies<br />

implication (2.1) is an l -group accord<strong>in</strong>g to Def<strong>in</strong>ition 2.3.<br />

From now on, let R be an l -group and = N<br />

N be the set of all mapp<strong>in</strong>gs, def<strong>in</strong>ed on N and<br />

tak<strong>in</strong>g values <strong>in</strong> N .<br />

We now <strong>in</strong>troduce two k<strong>in</strong>ds of convergence <strong>in</strong> l -groups. First of all, we beg<strong>in</strong> with the<br />

follow<strong>in</strong>g prelim<strong>in</strong>ary def<strong>in</strong>itions.<br />

Def<strong>in</strong>ition 2.12 A bounded double sequence ( a i, j) i, j <strong>in</strong> R is called a ( D) -sequence or regulator if<br />

a a i, jN<br />

and<br />

i, j i, j+<br />

1<br />

<br />

<br />

j=<br />

1<br />

a = 0iN<br />

.<br />

i, j<br />

Def<strong>in</strong>ition 2.13 A sequence ( p n) nis<br />

called an ( O) -sequence if pn pn+ 1 nN and<br />

In this case, we write also pn 0 .<br />

Def<strong>in</strong>ition 2.14 Given a sequence ( )<br />

n n<br />

<br />

<br />

n=<br />

1<br />

p<br />

n<br />

= 0 .<br />

r <strong>in</strong> R , we say that ( r ) ( D) -converges to an element<br />

r R if there exists a ( D) -sequence ( a , ) , <strong>in</strong> R , satisfy<strong>in</strong>g the follow<strong>in</strong>g condition:<br />

for all n n0<br />

, i j i j<br />

there exists an <strong>in</strong>teger n0<br />

such that<br />

<br />

<br />

| r r| a ,<br />

n i, () i<br />

i=<br />

1<br />

. In this case, we write ( )lim n n<br />

Def<strong>in</strong>ition 2.15 Given a sequence ( )<br />

n n<br />

D r = r.<br />

r R if there exists an ( O) -sequence ( p ) <strong>in</strong> R , such that<br />

In this case, we write ( )lim n n<br />

n n<br />

r <strong>in</strong> R , we say that ( r ) ( O) -converges to an element<br />

n n<br />

| rn r| pn n N .<br />

O r = r .<br />

Def<strong>in</strong>ition 2.16 Let R be a Dedek<strong>in</strong>d complete <strong>Riesz</strong> space, and ( a n) nbe<br />

a sequence <strong>in</strong> R. We<br />

call series associated with ( )<br />

n n<br />

n n<br />

a the sequence ( S ) , def<strong>in</strong>ed by sett<strong>in</strong>g<br />

n n<br />

S1<br />

= a1,<br />

<br />

Sn<br />

= Sn1+ an, n<br />

2,


42 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 42-51<br />

3 <strong>Kurzweil</strong> - <strong>Henstock</strong> <strong>Integral</strong> with Values <strong>in</strong> <strong>Riesz</strong><br />

Spaces<br />

Abstract: In this chapter we present the basic properties and results on the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral for <strong>Riesz</strong> spacevalued<br />

functions, def<strong>in</strong>ed on a bounded sub<strong>in</strong>terval of the real l<strong>in</strong>e. We prove the uniform convergence theorem, and<br />

<strong>in</strong>troduce also the <strong>Kurzweil</strong>-Stieltjes <strong>in</strong>tegral and some of its elementary properties.<br />

3.1 Def<strong>in</strong>ition and Elementary Properties<br />

One of the first problem <strong>in</strong> any <strong>in</strong>tegration theory with values <strong>in</strong> ordered <strong>spaces</strong> is impossibility to<br />

use the so-called -technique. Namely, <strong>in</strong> the real-valued case, if<br />

and , then , and there exists such that<br />

This is not true <strong>in</strong> partially ordered sets. E.g. let be the space of all real functions def<strong>in</strong>ed on<br />

with the usual order<strong>in</strong>g. Put<br />

where , , is def<strong>in</strong>ed by sett<strong>in</strong>g<br />

Then<br />

where<br />

If is considered as a constant function, then is the function def<strong>in</strong>ed by<br />

and there exists no element such that<br />

Of course, <strong>in</strong>stead of -technique, the double sequence technique proposed by D. H. Freml<strong>in</strong><br />

([130]) can be used. Consider first the classical case of the real l<strong>in</strong>e. Let<br />

double sequence of real numbers such that<br />

be a bounded<br />

Antonio Boccuto / Beloslav Riean / Marta Vrábelová<br />

All rights reserved - © 2009 <strong>Bentham</strong> <strong>Science</strong> Publishers Ltd.


<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> with Values <strong>in</strong> <strong>Riesz</strong> Spaces <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 43<br />

that is a -sequence or regulator <strong>in</strong> (see Chapter 2). Then to any and there exists<br />

such that for any we have . S<strong>in</strong>ce the <strong>in</strong>equality holds for any<br />

we have also<br />

Hence <strong>in</strong>stead of we can use the entity .<br />

As an illustration we show the def<strong>in</strong>ition of cont<strong>in</strong>uity of a function <strong>in</strong> a po<strong>in</strong>t<br />

. From now on, let be as <strong>in</strong> the previous chapter. The function is cont<strong>in</strong>uous at if<br />

and only if there exists a regulator <strong>in</strong> such that to any there exists such that<br />

whenever<br />

S<strong>in</strong>ce for the def<strong>in</strong>ition of the <strong>Kurzweil</strong> - <strong>Henstock</strong> <strong>in</strong>tegral the approach is advisable, we<br />

shall use the double sequence technique.<br />

The second problem is <strong>in</strong> the absence of the equality . It will be substitute by the famous<br />

Freml<strong>in</strong> lemma:<br />

Theorem 3.1 Let be a Dedek<strong>in</strong>d complete <strong>Riesz</strong> space, , , be a sequence of<br />

regulators <strong>in</strong> . Then to every , , there corresponds a regulator such that<br />

for any and .<br />

Proof: Put , , . Evidently is a -sequence, and<br />

Hence, we get:<br />

By the distributive law


44 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riean, M. Vrábelová<br />

This concludes the proof. <br />

<br />

Recall that there exists an -group-valued version of the Freml<strong>in</strong> lemma (see [130,228]). For two<br />

-sequences the correspond<strong>in</strong>g assertion is straightforward:<br />

Proposition 3.2 Let , be two -sequences. Then there exists a -sequence<br />

, such that<br />

for any .<br />

Proof: It is sufficient to put . <br />

Assumption 3.3 We shall assume that is a Dedek<strong>in</strong>d complete weakly -distributive <strong>Riesz</strong><br />

space.<br />

Def<strong>in</strong>ition 3.4 Let . If is a partition of , then the<br />

<strong>in</strong>tegral sum or Riemann sum is def<strong>in</strong>ed by the formula<br />

Let any map. A partition of is said to be -f<strong>in</strong>e<br />

if .<br />

The function is <strong>in</strong>tegrable (<strong>in</strong> the -sense) or -<strong>in</strong>tegrable on , if<br />

there exist and a<br />

such that<br />

-sequence such that to any there exists a map<br />

for any -f<strong>in</strong>e partition .<br />

Lemma 3.5 The element from Def<strong>in</strong>ition 3.4 is determ<strong>in</strong>ed uniquely.<br />

Proof: Let be such elements, be correspond<strong>in</strong>g -sequences, , and<br />

be -valued maps, def<strong>in</strong>ed on , such that<br />

for any -f<strong>in</strong>e partition of , . Put , and accord<strong>in</strong>g to<br />

Proposition 3.2. Then for any -f<strong>in</strong>e partition of we have:


52 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 52-61<br />

4 Double <strong>Integral</strong>s<br />

Abstract: We <strong>in</strong>troduce the theory of the double <strong>in</strong>tegrals for <strong>Riesz</strong> space-valued mapp<strong>in</strong>gs, def<strong>in</strong>ed on a bounded<br />

subrectangle of the Euclidean plane, and prove some versions of the Fub<strong>in</strong>i theorems. We deal also with some concepts<br />

of cont<strong>in</strong>uity for <strong>Riesz</strong> space-valued functions, related with these k<strong>in</strong>ds of results.<br />

In this chapter we def<strong>in</strong>e the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral for <strong>Riesz</strong> space-valued functions def<strong>in</strong>ed<br />

on bounded <strong>in</strong>tervals <strong>in</strong> and some types of the Fub<strong>in</strong>i theorem are presented (see also [267]).<br />

Similar theorems <strong>in</strong> the real case are obta<strong>in</strong>ed <strong>in</strong> [170, 188, 254].<br />

Let be a bounded 2-dimensional <strong>in</strong>terval of the set of the real numbers. A<br />

division of the <strong>in</strong>terval<br />

.<br />

is a set of non-overlapp<strong>in</strong>g bounded <strong>in</strong>tervals with<br />

Let . A -f<strong>in</strong>e partition of the <strong>in</strong>terval<br />

is a set of the type<br />

where<br />

for , are non-overlapp<strong>in</strong>g and .<br />

The existence of at least one -f<strong>in</strong>e partition of is guaranteed by the<br />

existence of a -f<strong>in</strong>e partition of and a -f<strong>in</strong>e partition of (see subsection<br />

"Compound partitions").<br />

4.1 Def<strong>in</strong>ition of the Double <strong>Integral</strong><br />

Let be a Dedek<strong>in</strong>d complete weakly -distributive <strong>Riesz</strong> space, and .<br />

Def<strong>in</strong>ition 4.1 A function is called -<strong>in</strong>tegrable (<strong>in</strong> the <strong>Kurzweil</strong>-<br />

<strong>Henstock</strong> sense) if there exist and a regulator <strong>in</strong> such that for every there is<br />

such that<br />

for every -f<strong>in</strong>e partition<br />

The element we will called the double <strong>in</strong>tegral of on , and we denote it by<br />

or more simply<br />

Antonio Boccuto / Beloslav Riean / Marta Vrábelová<br />

All rights reserved - © 2009 <strong>Bentham</strong> <strong>Science</strong> Publishers Ltd.


Double <strong>Integral</strong>s <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 53<br />

We will omit <strong>in</strong> proofs and examples.<br />

Furthermore, we denote<br />

<br />

, and so on.<br />

Remark 4.2 The proofs of uniqueness and of the elementary properties of the double -<br />

<strong>in</strong>tegral are similar as the ones <strong>in</strong> Section 3.<br />

Example 4.3 Let be a bounded <strong>in</strong>terval, We show that the<br />

function where is the characteristic function of , is -<strong>in</strong>tegrable on and<br />

First we def<strong>in</strong>e the regulator by sett<strong>in</strong>g<br />

Let be arbitrary. Take . There exist an open <strong>in</strong>terval and a closed<br />

<strong>in</strong>terval such that .<br />

For def<strong>in</strong>e <strong>in</strong> such a way that<br />

For def<strong>in</strong>e <strong>in</strong> such a way that<br />

Take any arbitrary -f<strong>in</strong>e partition of . Then<br />

We have non-overlapp<strong>in</strong>g closed <strong>in</strong>tervals fulfill<strong>in</strong>g and, from the f<strong>in</strong>ite<br />

additivity of on the set of rectangles (we omit the proof of that fact <strong>in</strong> this place), we get:<br />

Therefore<br />

Example 4.4 Let and . Hence, there is a<br />

regulator <strong>in</strong> such that for every we have


54 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riean, M. Vrábelová<br />

and<br />

<br />

(4.1)<br />

(4.2)<br />

whenever . Denote Then , s<strong>in</strong>ce is Dedek<strong>in</strong>d complete.<br />

Let . Put<br />

(see Figure 4.1).<br />

Fig. 4.1 The sets<br />

Def<strong>in</strong>e the function on by the formula<br />

Hence if and at the other po<strong>in</strong>ts <strong>in</strong> . We will show<br />

that is -<strong>in</strong>tegrable on and


62 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 62-70<br />

5 <strong>Kurzweil</strong> - <strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> Topological Spaces<br />

Abstract: We deal with the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral for functions def<strong>in</strong>ed <strong>in</strong> an abstract compact topological space<br />

and tak<strong>in</strong>g values <strong>in</strong> <strong>Riesz</strong> <strong>spaces</strong>.<br />

We <strong>in</strong>troduce the theory and the fundamental properties, and <strong>in</strong> particular we prove the monotone convergence theorem.<br />

5.1 Elementary Properties<br />

In the chapter we shall work with a compact topological space <strong>in</strong>stead of a compact <strong>in</strong>terval<br />

.<br />

Assumption 5.1 We assume that is a Hausdorff compact topological space, and that there<br />

are: a family of Borel subsets of such that and closed under <strong>in</strong>tersections, and a<br />

mapp<strong>in</strong>g<br />

Def<strong>in</strong>ition 5.2 We say that is additive, if<br />

whenever .<br />

Let be the -algebra of all Borel subsets of . We say that is regular, if to any<br />

and any there exist compact and open such that and<br />

.<br />

Def<strong>in</strong>ition 5.3 A gauge on is a mapp<strong>in</strong>g assign<strong>in</strong>g to each an open<br />

neighborhood .<br />

Example 5.4 Let , be a map. Let be the usual topology on the real l<strong>in</strong>e.<br />

Put . Then is a gauge <strong>in</strong> the sense of Def<strong>in</strong>ition 5.3.<br />

Def<strong>in</strong>ition 5.5 A partition of is a f<strong>in</strong>ite collection of couples such that<br />

(i) ;<br />

(ii) ;<br />

(iii) .<br />

A collection satisfy<strong>in</strong>g axioms (ii) and (iii), but not necessarily (i), is called decomposition of .<br />

The partition or decomposition is -f<strong>in</strong>e , if .<br />

Def<strong>in</strong>ition 5.6 We say that is separat<strong>in</strong>g, if there exists a sequence of partitions such<br />

that is a ref<strong>in</strong>ement of and for any there exist and<br />

such that, if for some , then .<br />

Antonio Boccuto / Beloslav Riean / Marta Vrábelová<br />

All rights reserved - © 2009 <strong>Bentham</strong> <strong>Science</strong> Publishers Ltd.


<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> Topological Spaces <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 63<br />

Example 5.7 The compact <strong>in</strong>terval with the usual topology is a Hausdorff compact<br />

topological space. The family of all compact sub<strong>in</strong>tervals (<strong>in</strong>clud<strong>in</strong>g s<strong>in</strong>gletons and ) is<br />

separat<strong>in</strong>g, and def<strong>in</strong>ed by is additive and regular.<br />

Lemma 5.8 If is separat<strong>in</strong>g, then to any gauge there exists a -f<strong>in</strong>e partition.<br />

Proof: Let us consider . We want to prove that the space is decomposable, i.e. that there<br />

exists a partition of such that If not, then one of the<br />

elements of (denote it by ) is not decomposable. Similarly there is an <strong>in</strong>decomposable<br />

, etc. Evidently Let . S<strong>in</strong>ce is separat<strong>in</strong>g,<br />

S<strong>in</strong>ce , there exists such that . But then the s<strong>in</strong>gleton is a<br />

partition of . This is a contradiction with the assumption that is <strong>in</strong>decomposable. <br />

Remark 5.9 If is a compact metric space, is a semir<strong>in</strong>g of subsets of such that to any<br />

and every neighborhood of there exists such that (where,<br />

given any subset of any topological space, denotes its <strong>in</strong>terior <strong>in</strong> the topological sense) and<br />

is separat<strong>in</strong>g, then <strong>in</strong> correspondence with any set<br />

also [217], Lemma 1.2., p. 154 and Proposition 1.7., p. 156).<br />

there exists a -f<strong>in</strong>e partition (see<br />

Def<strong>in</strong>ition 5.10 (see also [217]) A function is -<strong>in</strong>tegrable (or, <strong>in</strong> short,<br />

<strong>in</strong>tegrable) if there exists such that to any there exist a gauge such that<br />

for every partition . Here the entity<br />

is called Riemann sum or <strong>in</strong>tegral sum.<br />

Evidently the number is determ<strong>in</strong>ed uniquely. It will be denoted by<br />

Proposition 5.11 The <strong>in</strong>tegral is a l<strong>in</strong>ear positive functional.<br />

Proof: The l<strong>in</strong>earity follows by the identity<br />

The positivity follows by the implication<br />

Proposition 5.12 (Bolzano-Cauchy condition) A function is <strong>in</strong>tegrable if and only if the<br />

follow<strong>in</strong>g condition holds:<br />

<br />

To any there exists a gauge such that


64 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riean, M. Vrábelová<br />

for every two partitions .<br />

Proof: The necessity of this condition is evident. We now turn to the sufficiency. If the condition is<br />

satisfied, we can put . So, there exists a gauge such that<br />

for every two partitions . Put<br />

Then there exists exactly one that belongs to the set For every choose such<br />

that and put . Then for each partition we obta<strong>in</strong><br />

Def<strong>in</strong>ition 5.13 A function is said to be -<strong>in</strong>tegrable (or, <strong>in</strong> short, <strong>in</strong>tegrable) on a<br />

set if there exists such that to any there exist a gauge such that<br />

for every partition of .<br />

The element is denoted by .<br />

Proposition 5.14 If f is <strong>in</strong>tegrable on , , and , then is <strong>in</strong>tegrable<br />

on too.<br />

Proof: We shall use the Bolzano-Cauchy condition. To any there exists a gauge<br />

such that<br />

for every . Put and . Choose and def<strong>in</strong>e ,<br />

. Then so that


6 Convergence Theorems<br />

<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 71-83 71<br />

Abstract: We cont<strong>in</strong>ue to <strong>in</strong>vestigate the topics of Chapter 5, follow<strong>in</strong>g the approach there <strong>in</strong>troduced, and prove some<br />

versions of the <strong>Henstock</strong> Lemma, the Beppo Levi and the Lebesgue dom<strong>in</strong>ated convergence theorem.<br />

Note that the <strong>in</strong>volved measures and the doma<strong>in</strong> of our functions can be even unbounded.<br />

6.1 Elementary Properties<br />

Antonio Boccuto / Beloslav Riean / Marta Vrábelová<br />

All rights reserved - © 2009 <strong>Bentham</strong> <strong>Science</strong> Publishers Ltd.<br />

<br />

In the book we have exposed the elementary theory of the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral (Chapter 1),<br />

then basic facts about the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral for functions from a compact <strong>in</strong>terval to a<br />

<strong>Riesz</strong> space (Chapter 3). Of course, <strong>in</strong> Chapter 5 there have been considered functions def<strong>in</strong>ed on a<br />

compact topological space. In this chapter we deal with convergence theorems (monotone<br />

convergence theorem and Lebesgue dom<strong>in</strong>ated convergence theorem) for the <strong>Kurzweil</strong>-<strong>Henstock</strong><br />

<strong>in</strong>tegral <strong>in</strong> an abstract sett<strong>in</strong>g, for functions def<strong>in</strong>ed <strong>in</strong> a compact topological space , satisfy<strong>in</strong>g<br />

suitable properties, and with values <strong>in</strong> a Dedek<strong>in</strong>d complete <strong>Riesz</strong> space, with respect to a positive<br />

<strong>Riesz</strong> space-valued measure , which can assume even the value . A particular case is<br />

an <strong>in</strong>terval (possibly unbounded) of the extended real l<strong>in</strong>e, or the whole of , and<br />

the Lebesgue measure (this case was <strong>in</strong>vestigated <strong>in</strong> [26]). We cont<strong>in</strong>ue the <strong>in</strong>vestigation started <strong>in</strong><br />

[24], <strong>in</strong> which is -valued, and <strong>in</strong> which some other k<strong>in</strong>ds of convergence theorems were<br />

demonstrated. Our results given here are proved <strong>in</strong> [29] and extend the ones <strong>in</strong> [227], Chapter 5,<br />

which were proved <strong>in</strong> the case <strong>in</strong> which is f<strong>in</strong>ite, and the ones of [170], which were proved <strong>in</strong><br />

the case , where is as above, and all the <strong>in</strong>volved <strong>Riesz</strong> <strong>spaces</strong> co<strong>in</strong>cide with the<br />

(eventually extended) real l<strong>in</strong>e. A similar <strong>Kurzweil</strong>-<strong>Henstock</strong> type <strong>in</strong>tegral was <strong>in</strong>vestigated <strong>in</strong> [36]<br />

for Banach space-valued maps.<br />

From now on, <strong>in</strong> this chapter we shall always suppose that is a Dedek<strong>in</strong>d complete weakly -<br />

distributive <strong>Riesz</strong> space.<br />

Assumption 6.1 Let , be as <strong>in</strong> Chapter 5, and let us consider a positive mapp<strong>in</strong>g<br />

Def<strong>in</strong>ition 6.2 We say that is additive, if<br />

whenever .<br />

Let be the -algebra of all Borel subsets of . We say that a positive set function<br />

is regular, if to any there exists a regulator such that for every there exist<br />

compact, open and such that , .<br />

The concepts of gauge, partition, decomposition, -f<strong>in</strong>eness and separat<strong>in</strong>g family are given<br />

analogously as <strong>in</strong> Chapter 5.


72 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riean, M. Vrábelová<br />

Assumptions 6.3 Let , , be three Dedek<strong>in</strong>d complete <strong>Riesz</strong> <strong>spaces</strong>. We say that<br />

is a product triple if there exists a map<br />

conditions given at the end of Chapter 2 and such that<br />

which we will call product, satisfy<strong>in</strong>g the<br />

<br />

r , and , then .<br />

We will write often <strong>in</strong>stead of . A Dedek<strong>in</strong>d complete <strong>Riesz</strong> space is called an algebra if<br />

is a product triple.<br />

We always assume that is a product triple and that is weakly -distributive.<br />

Furthermore, we add to two extra elements, and , extend<strong>in</strong>g order<strong>in</strong>g and operations <strong>in</strong> a<br />

natural way, and denote .<br />

We now give our def<strong>in</strong>ition of <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegrability. We suppose that is<br />

an additive positive regular measure. If is a partition or a decomposition of<br />

a set , and , then we def<strong>in</strong>e the Riemann sum as follows:<br />

if the sum exists <strong>in</strong> , with the conventions that and that only the ’s with<br />

are <strong>in</strong>volved. The po<strong>in</strong>ts , , are called tags.<br />

Def<strong>in</strong>ition 6.4 A function is -<strong>in</strong>tegrable (or, <strong>in</strong> short, <strong>in</strong>tegrable) if there exist<br />

and a regulator such that there exists a gauge such that<br />

whenever is a -f<strong>in</strong>e partition of .<br />

Evidently the number is determ<strong>in</strong>ed uniquely. It will be denoted by<br />

(6.1)<br />

It is easy to check that, even <strong>in</strong> this context, the <strong>in</strong>volved <strong>in</strong>tegral is a l<strong>in</strong>ear positive functional.<br />

Def<strong>in</strong>ition 6.5 A function is -<strong>in</strong>tegrable (or, <strong>in</strong> short, <strong>in</strong>tegrable) on a set<br />

if there exist and a regulator such that there exists a gauge such that<br />

whenever is a -f<strong>in</strong>e partition of .<br />

(6.2)


Convergence Theorems <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 73<br />

The element is denoted by . When we will say simply "<strong>in</strong>tegrable", we will <strong>in</strong>tend<br />

"<strong>in</strong>tegrable on ".<br />

<br />

We now state the Bolzano-Cauchy condition.<br />

Theorem 6.6 A map is -<strong>in</strong>tegrable on if and only if there exists a<br />

regulator<br />

we have<br />

such that, , a gauge such that for all -f<strong>in</strong>e partitions , of<br />

The proof is similar to the one of [227], Proposition 5.2.9, pp. 77-79.<br />

Proposition 6.7 If , , and is <strong>in</strong>tegrable on , then is<br />

<strong>in</strong>tegrable on and on too, and<br />

The proof is similar to the one of [227], Proposition 5.2.10, pp. 79-80 (see also Chapter 5,<br />

Propositions 5.14 and 5.15).<br />

By <strong>in</strong>duction, it is possible to prove the follow<strong>in</strong>g:<br />

Proposition 6.8 If , , , and , whenever and<br />

is <strong>in</strong>tegrable on , then is <strong>in</strong>tegrable on for every , and<br />

(see also Chapter 5, Proposition 5.16).<br />

The follow<strong>in</strong>g result holds (see also [227], Proposition 5.2.11, pp. 80-81):<br />

Theorem 6.9 Let be the class of all Borel sets of , be positive, additive and<br />

regular, , with . Let , and (def<strong>in</strong>ed by the relation , if<br />

and , if ). Then is <strong>in</strong>tegrable, and<br />

Proof: First of all, assume . By regularity of on there exists a -sequence<br />

such that for every there exist an open set and a compact set , , such that<br />

S<strong>in</strong>ce is compact and is open, there exists a gauge such that ,<br />

, . Take any partition ,<br />

. Then


84 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 84-110<br />

7 Improper <strong>Integral</strong><br />

Abstract: In this chapter we deal with the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral for functions def<strong>in</strong>ed <strong>in</strong> (possibly unbounded)<br />

sub<strong>in</strong>tervals of the extended real l<strong>in</strong>e.<br />

We beg<strong>in</strong> with real-valued maps and after we consider <strong>Riesz</strong> space-valued mapp<strong>in</strong>gs.<br />

All the basic properties are proved, together with Hake convergence-type theorems.<br />

7.1 Real Valued Case<br />

The aim of this chapter is to generalize the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral to functions def<strong>in</strong>ed on an<br />

unbounded <strong>in</strong>terval of the extended real l<strong>in</strong>e (and later, more generally, on a suitable locally<br />

compact topological space) and with values <strong>in</strong> R , <strong>in</strong> a Banach space and <strong>in</strong> a <strong>Riesz</strong> space, and to<br />

construct a type of <strong>in</strong>tegral conta<strong>in</strong><strong>in</strong>g the improper Riemann <strong>in</strong>tegral under suitable hypotheses.<br />

The case of real-valued functions was <strong>in</strong>vestigated <strong>in</strong> [170]. The cases of Banach- and <strong>Riesz</strong>-spacevalued<br />

functions are topics of our research (see [36] and [26]). Moreover ([23, 24]), we considered<br />

also the case of real-valued or <strong>Riesz</strong>-space-valued functions, def<strong>in</strong>ed on abstract locally compact<br />

topological <strong>spaces</strong>, satisfy<strong>in</strong>g some suitable properties. The case of the (extended) real l<strong>in</strong>e is<br />

<strong>in</strong>cluded <strong>in</strong> this general case; however, for the sake of clearness, we consider and <strong>in</strong>vestigate it<br />

separately at the beg<strong>in</strong>n<strong>in</strong>g of this chapter, even because - <strong>in</strong> this case - we proved more detailed<br />

results.<br />

We beg<strong>in</strong> with the case of real-valued functions, def<strong>in</strong>ed on (possibly) unbounded sub<strong>in</strong>tervals of<br />

the extended real l<strong>in</strong>e. We will report <strong>in</strong> a more detailed way some proofs of [170]: the technique<br />

here used will be useful also <strong>in</strong> the case of Banach- and <strong>Riesz</strong>-space-valued functions.<br />

We will construct a type of <strong>in</strong>tegral (with respect to the Lebesgue measure def<strong>in</strong>ed on<br />

sub<strong>in</strong>tervals of the extended real l<strong>in</strong>e, not necessarily bounded), conta<strong>in</strong><strong>in</strong>g the improper Riemann<br />

<strong>in</strong>tegral. From now on, we denote by [ A, B]<br />

a closed <strong>in</strong>terval or halfl<strong>in</strong>e conta<strong>in</strong>ed <strong>in</strong> % R , or the<br />

whole of % R , and by Δ the set of all positive real-valued functions, def<strong>in</strong>ed on [ A, B]<br />

. Moreover,<br />

given a measurable set E ⊂ % R , we denote by | E | its Lebesgue measure (this quantity can be f<strong>in</strong>ite<br />

or +∞ ) . Throughout this paragraph, our <strong>in</strong>tegral deals with real-valued functions def<strong>in</strong>ed on [ A, B]<br />

,<br />

but it can be <strong>in</strong>vestigated analogously if we take functions def<strong>in</strong>ed on R or on halfl<strong>in</strong>es of the type<br />

[ a,+∞ ) or ( −∞, a]<br />

, with a ∈ R .<br />

Def<strong>in</strong>itions 7.1 A decomposition or subpartition Π of [ A, B]<br />

is a set of pairs ( Ik, ξk)<br />

, k = 1,<br />

…, p,<br />

such that ξk ∈ Ik<br />

∀ k , and the I k ’s are non-overlapp<strong>in</strong>g closed <strong>in</strong>tervals, conta<strong>in</strong>ed <strong>in</strong> [ A, B]<br />

. A<br />

p<br />

partition Π= {( Ik, ξk)<br />

: k = 1, …, p}<br />

of [ A, B]<br />

is a subpartition of [ A, B]<br />

with U k= 1 Ik = [ A, B]<br />

.<br />

A gauge is a map γ def<strong>in</strong>ed <strong>in</strong> [ A, B]<br />

and tak<strong>in</strong>g values <strong>in</strong> the set of all open <strong>in</strong>tervals <strong>in</strong> % R,<br />

such that ξ ∈ γξ ( ) for every ξ ∈ [ A, B]<br />

and γ ( ξ ) is a bounded open <strong>in</strong>terval for every<br />

ξ ∈R ∩ [ A, B]<br />

. Given a gauge γ , we will say that a partition or decomposition<br />

Π= {( Ik, ξk)<br />

: k = 1, … , p}<br />

of [ A, B]<br />

is γ -f<strong>in</strong>e if Ik ⊂ γ ( ξk)<br />

∀ k = 1,<br />

…, p.<br />

Given a bounded <strong>in</strong>terval<br />

+<br />

[ ab , ] ⊂R and a map δ : [ ab , ] →R , a partition or decomposition Π = {( I , ξ ) : k = 1, … , p}<br />

of<br />

[ ab , ] is said to be δ -f<strong>in</strong>e if I ⊂( ξ − δξ ( ) , ξ + δξ ( )) ∀ k = 1,<br />

…, p.<br />

k k k k k<br />

Antonio Boccuto / Beloslav Riečan / Marta Vrábelová<br />

All rights reserved - © 2009 <strong>Bentham</strong> <strong>Science</strong> Publishers Ltd.<br />

k k


Improper <strong>Integral</strong> <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 85<br />

We note that, if I k is an unbounded <strong>in</strong>terval, then the element ξ k associated with I k is<br />

necessarily +∞ or −∞ : otherwise γ ( ξ k ) should be a bounded <strong>in</strong>terval and conta<strong>in</strong> an unbounded<br />

<strong>in</strong>terval: contradiction.<br />

Given any partition or decomposition Π = {( Ik, ξk)<br />

: k = 1, …, p}<br />

of [ A, B]<br />

and a function<br />

f : [ A, B]<br />

→R , we call Riemann sum of f (and we write ∑ f ) the quantity<br />

p<br />

∑ | Ik | f( ξk)<br />

,<br />

(7.1)<br />

k = 1<br />

where <strong>in</strong> the sum <strong>in</strong> (7.1) only the terms for which I k is a bounded <strong>in</strong>terval are <strong>in</strong>cluded. This can<br />

be required by simply postulat<strong>in</strong>g it or by def<strong>in</strong><strong>in</strong>g the measure of an unbounded <strong>in</strong>terval as +∞ , by<br />

requir<strong>in</strong>g f( +∞ ) = f(<br />

−∞ ) = 0 and by means of the convention 0( ⋅ +∞ ) = 0(see<br />

also [170], p. 65).<br />

We now formulate our def<strong>in</strong>ition of <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral for functions def<strong>in</strong>ed on [ A, B]<br />

.<br />

Def<strong>in</strong>ition 7.2 We say that a function f : [ A, B]<br />

→R is <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegrable (<strong>in</strong> short<br />

( KH ) -<strong>in</strong>tegrable) on [ A, B]<br />

if there exists an element I ∈ R such that ∀ ε > 0 there exist a<br />

function δ ∈Δ and a positive real number P such that<br />

∑ f − I ≤ ε<br />

(7.2)<br />

Π<br />

whenever Π= {( Ik, ξk)<br />

: k = 1, … , p}<br />

is a δ -f<strong>in</strong>e partition of any bounded <strong>in</strong>terval [ ab , ] with<br />

[ ab , ] ⊃ [ AB , ] ∩[ − PP , ] and [ ab , ] ⊂ [ AB , ] . In this case we say that I is the ( KH ) -<strong>in</strong>tegral of f ,<br />

and we denote the element I by the symbol ( ) B<br />

KH ∫ f or more simply<br />

A<br />

B<br />

∫ f . Later we will prove<br />

A<br />

that our <strong>in</strong>tegral is well-def<strong>in</strong>ed, that is such an I is uniquely determ<strong>in</strong>ed.<br />

We now prove the follow<strong>in</strong>g characterization of ( KH ) -<strong>in</strong>tegrability:<br />

Theorem 7.3 A function f : [ A, B]<br />

→R is ( KH ) -<strong>in</strong>tegrable if and only if there exists J ∈ R such<br />

that ∀ ε > 0 there exists a gauge γ such that<br />

∑ f − J ≤ ε<br />

(7.3)<br />

Π<br />

whenever Π= {( I , ξ ) : k = 1, … , p}<br />

is a γ -f<strong>in</strong>e partition of [ A, B]<br />

, and <strong>in</strong> this case we have<br />

∫<br />

B<br />

A<br />

f J =<br />

.<br />

k k<br />

Proof: We beg<strong>in</strong> with the "only if" part. By hypothesis, ∀ ε > 0 there exist a function δ ∈Δ and a<br />

positive real number P such that (7.2) holds. We now def<strong>in</strong>e on [ A, B]<br />

a gauge γ <strong>in</strong> the follow<strong>in</strong>g<br />

way:<br />

⎧(<br />

ξ − δ( ξ) , ξ + δ( ξ)) if ξ∈<br />

[ AB , ] ∩ R,<br />

⎪<br />

γξ ( ) = ⎨[<br />

−∞,− P) if ξ=−∞<br />

andA=−∞,<br />

⎪<br />

⎩(<br />

P,+∞ ] if ξ =+∞ andB=+∞.<br />

We observe that every γ -f<strong>in</strong>e partition Π = {( Ik, ξk)<br />

: k = 1, … , p}<br />

of [ A, B]<br />

is such that Ik ⊂ γ ( ξk)<br />

∀ k = 1,<br />

…, p.<br />

In the case A =−∞, B = +∞ , the partition Π conta<strong>in</strong>s two unbounded <strong>in</strong>tervals,<br />

which we call J and K : of course, if <strong>in</strong>f J = −∞ and sup K = +∞ , then the ξ k ’s associated with J<br />

Π


86 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riečan, M. Vrábelová<br />

and K are −∞ and +∞ respectively. Then, s<strong>in</strong>ce Π is γ -f<strong>in</strong>e, we have J ⊂γ( −∞ ) and<br />

K ⊂ γ ( +∞ ) . Then J ⊂[ −∞,− P)<br />

and K ⊂ ( P,+∞<br />

] . So, if a= sup J and b= <strong>in</strong>f K , then [ ab , ] is a<br />

bounded <strong>in</strong>terval, conta<strong>in</strong><strong>in</strong>g [ − P, P]<br />

. If Π ′ is the restriction of Π to [ ab , ] , then Π ′ is δ -f<strong>in</strong>e, and<br />

by construction we get<br />

f = f .<br />

∑ ∑ (7.4)<br />

Π′ Π<br />

In this case, the assertion follows from (7.2) and (7.4).<br />

In the case A∈ R , B =+∞, the partition Π conta<strong>in</strong>s only an unbounded <strong>in</strong>terval K , with<br />

sup K =+∞. Let P be associated with K as above, and b= <strong>in</strong>f K : we have P ≤ b . We note that,<br />

without loss of generality, P can be taken greater than | A | . Thus, [ A, b]<br />

is a bounded <strong>in</strong>terval,<br />

conta<strong>in</strong><strong>in</strong>g [ − P, P]<br />

, and the assertion follows by proceed<strong>in</strong>g as <strong>in</strong> the previous case. The case<br />

A =−∞, B ∈R is analogous to the previous one. F<strong>in</strong>ally, if [ A, B]<br />

is bounded, then the assertion is<br />

straightforward, because <strong>in</strong> this case the number P can be taken greater than max( | A |,| B | ) and, of<br />

course, (7.2) holds even <strong>in</strong> the case [ ab , ] = [ AB , ] . This concludes the proof of the "only if" part.<br />

We now turn to the "if" part. By hypothesis, we know that ∀ ε > 0 there exists a gauge γ<br />

satisfy<strong>in</strong>g (7.3). By def<strong>in</strong>ition of gauge, there exist δ1, δ2∈Δ<br />

such that<br />

γ ( ξ) = ( ξ − δ1( ξ) , ξ + δ2( ξ)) ∀ξ∈ [ AB , ] ∩ R .<br />

For such ξ ’s, let δ ( ξ) = m<strong>in</strong>{ δ1( ξ), δ2( ξ)}<br />

. Moreover, if +∞ and −∞ belong to [ A, B]<br />

, and<br />

∗<br />

∗<br />

γ ( −∞ ) = [ −∞, P1<br />

) , γ ( +∞ ) = ( P2<br />

, +∞ ] , put P1 m<strong>in</strong>{ P1 , 1}<br />

∗<br />

= − , P2 max{ P2 ,1}<br />

∗<br />

= , P = max{ − P1, P2}<br />

: we<br />

note that, <strong>in</strong> the case A∈ R (resp. B ∈ R), P can be chosen greater than | A | (resp. | B | );<br />

moreover, set δ ( −∞ ) = δ ( +∞ ) = P . Let now [ ab , ] ⊂ [ AB , ] be any bounded <strong>in</strong>terval, conta<strong>in</strong><strong>in</strong>g<br />

[ A, B] ∩[ − P, P]<br />

, and Π = {( Ik, ξk)<br />

: k = 1, … , p}<br />

be a δ -f<strong>in</strong>e partition of [ ab , ] . Let Π ′ be that<br />

partition of [ A, B]<br />

, whose elements are the ones of Π with the addition of ([ A, a] , A)<br />

, if A = −∞ ,<br />

and ([ bB , ] , B)<br />

, if B =+∞: we note that Π ′ is γ -f<strong>in</strong>e. This follows from the fact that, if ( Ik, ξk)<br />

is<br />

any element of Π , then<br />

Ik ⊂( ξk − δ( ξk) , ξk + δ( ξk)) ⊂( ξk − δ1( ξk) , ξk + δ2( ξk)) = γ( ξk)<br />

,<br />

and from the follow<strong>in</strong>g <strong>in</strong>clusions:<br />

∗<br />

( b,+∞] ⊂ ( P,+∞] ⊂ ( P2,+∞] ⊂ ( P2,+∞ ] = γ ( +∞ ) ,<br />

∗<br />

[ −∞, a) ⊂ [ −∞, P) ⊂ [ −∞, P1) ⊂ [ −∞, P1 ) = γ ( −∞ ) .<br />

Then, tak<strong>in</strong>g <strong>in</strong>to account that the Riemann sum concern<strong>in</strong>g the partition Π ′ is done without<br />

consider<strong>in</strong>g the unbounded <strong>in</strong>tervals, we get f = f<br />

∑ ∑ . From this and (7.3) the assertion<br />

Π′ Π<br />

follows, by proceed<strong>in</strong>g analogously as at the end of the proof of the converse implication. This<br />

concludes the proof of the theorem.<br />

Remark 7.4 We note that the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral is well-def<strong>in</strong>ed, that is there exists at<br />

most one element I , satisfy<strong>in</strong>g condition (7.3): <strong>in</strong>deed, if ∃ such two elements I , J , then ∀ ε > 0<br />

∃ two gauges γ 1 , γ 2 such that, for each γ1 -f<strong>in</strong>e partition Π and for every γ 2 -f<strong>in</strong>e partition Π ′ of<br />

[ A, B]<br />

we have


8 Choquet and ipo <strong>Integral</strong>s<br />

<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 111-133 111<br />

Abstract: In this chapter we <strong>in</strong>troduce some <strong>in</strong>tegrals for real-valued maps with respect to <strong>Riesz</strong> space-valued set<br />

functions, which are not necessarily f<strong>in</strong>itely additive, but <strong>in</strong> general can be simply only <strong>in</strong>creas<strong>in</strong>g. First we deal with<br />

the ipo (symmetric) <strong>in</strong>tegral and prove the monotone and Lebesgue dom<strong>in</strong>ated convergence theorems, Fatou’s lemma<br />

and the submodular theorem.<br />

Moreover we <strong>in</strong>troduce the Choquet (asymmetric) <strong>in</strong>tegral, giv<strong>in</strong>g <strong>in</strong> particular some applications to the weak and<br />

strong laws of large numbers <strong>in</strong> the context of <strong>Riesz</strong> <strong>spaces</strong>.<br />

<br />

8.1 Symmetric <strong>Integral</strong><br />

In this chapter we deal with some recent research and results about Choquet-type <strong>in</strong>tegrals for realvalued<br />

(or extended real-valued) functions, with respect to set functions with values <strong>in</strong> a<br />

Dedek<strong>in</strong>d complete <strong>Riesz</strong> space , and which can be -additive, f<strong>in</strong>itely additive or simply only<br />

<strong>in</strong>creas<strong>in</strong>g. In the literature, <strong>in</strong> the case , there are substantially two k<strong>in</strong>ds of <strong>in</strong>tegrals <strong>in</strong> this<br />

context: the symmetric and the asymmetric <strong>in</strong>tegral (see also [73]). Here we <strong>in</strong>vestigate <strong>in</strong> detail<br />

only the symmetric <strong>in</strong>tegral, because our ma<strong>in</strong> recent researches <strong>in</strong> this topic deal with the case <strong>in</strong><br />

which is f<strong>in</strong>itely additive (here the two <strong>in</strong>tegrals will co<strong>in</strong>cide) and, when is only monotone,<br />

just (ma<strong>in</strong>ly) with the symmetric <strong>in</strong>tegral.<br />

In [32] we <strong>in</strong>troduced a "monotone-type" (that is, Choquet-type) <strong>in</strong>tegral for real-valued maps,<br />

with respect to f<strong>in</strong>itely additive positive set functions, with values <strong>in</strong> a Dedek<strong>in</strong>d complete <strong>Riesz</strong><br />

space. In [98], a Choquet-type <strong>in</strong>tegral for real-valued functions with respect to <strong>Riesz</strong>-space-valued<br />

"capacities" , that is monotone set functions (not necessarily f<strong>in</strong>itely additive), is <strong>in</strong>vestigated.<br />

We <strong>in</strong>troduce a ipo-type <strong>in</strong>tegral, that is "symmetric" <strong>in</strong>tegral, for real-valued functions with<br />

respect to <strong>Riesz</strong>-space-valued capacities, we <strong>in</strong>vestigate the fundamental properties and prove some<br />

convergence theorems (for real-valued capacities see also [249] and [204], pp. 152-176).<br />

Throughout this paragraph, we always suppose that is a Dedek<strong>in</strong>d complete <strong>Riesz</strong> space. In<br />

some suitable cases, we add to two extra elements, which we call and , extend<strong>in</strong>g<br />

order<strong>in</strong>g and operations, hav<strong>in</strong>g the same role as the usual and with the real numbers (see<br />

also [15, 136]). We denote with the symbol the set .<br />

We now extend to general directed nets the concept of -convergence.<br />

A directed net is called -net if , that is if it is decreas<strong>in</strong>g and . We<br />

say that the directed net is -convergent to , if<br />

and <strong>in</strong> this case we will write<br />

Def<strong>in</strong>ition 8.1 Let be an arbitrary nonempty set, and The class<br />

is called the upper set system of<br />

Antonio Boccuto / Beloslav Riean / Marta Vrábelová<br />

All rights reserved - © 2009 <strong>Bentham</strong> <strong>Science</strong> Publishers Ltd.


112 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riean, M. Vrábelová<br />

Def<strong>in</strong>ition 8.2 We say that a class of elements of is comonotonic if is a cha<strong>in</strong>, or<br />

equivalently, if, for each pair of there is no pair of elements , such that<br />

and (see [73, 204]).<br />

We beg<strong>in</strong> with recall<strong>in</strong>g the Choquet <strong>in</strong>tegral, <strong>in</strong>troduced <strong>in</strong> [98], and we <strong>in</strong>troduce and <strong>in</strong>vestigate<br />

the ipo (that is the symmetric Choquet) <strong>in</strong>tegral for (extended) real-valued functions with respect<br />

to <strong>Riesz</strong> space-valued capacities.<br />

Def<strong>in</strong>ition 8.3 Let be any nonempty set, and be a -algebra (We suppose this for<br />

the sake of simplicity, though several results rema<strong>in</strong> true if we consider more general structures).<br />

We say that a set function is a capacity if and whenever<br />

is said to be submodular if<br />

supermodular, if<br />

subadditive, if<br />

superadditive, if<br />

<br />

An -valued capacity is said to be cont<strong>in</strong>uous from below if for every <strong>in</strong>creas<strong>in</strong>g sequence<br />

of elements of we have<br />

cont<strong>in</strong>uous from above, if for every decreas<strong>in</strong>g sequence of elements of we have<br />

cont<strong>in</strong>uous, if it is cont<strong>in</strong>uous both from below and from above.<br />

A map called mean (or f<strong>in</strong>itely additive set function) if and<br />

whenever It is easy to check that every mean is a capacity,<br />

but the converse is <strong>in</strong> general not true. We say that a set function is a measure or that is -<br />

additive if it is a cont<strong>in</strong>uous mean. We say that a map is measurable if ,<br />

. A real-valued measurable map is called random variable too. Similarly as <strong>in</strong> [32], given a<br />

measurable mapp<strong>in</strong>g and a capacity , for all set:<br />

and, for every , let .<br />

We now <strong>in</strong>troduce the Choquet <strong>in</strong>tegral for non-negative functions with respect to <strong>Riesz</strong> spacevalued<br />

capacities (see also [33, 98]).


Choquet and ipo <strong>Integral</strong>s <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 113<br />

Def<strong>in</strong>ition 8.4 A measurable non-negative map<br />

exists <strong>in</strong> the quantity<br />

<br />

is said to be Choquet <strong>in</strong>tegrable if there<br />

where , , and is the Riemann <strong>in</strong>tegral for <strong>Riesz</strong>-space-valued maps,<br />

def<strong>in</strong>ed on an <strong>in</strong>terval of the real l<strong>in</strong>e, as <strong>in</strong> Chapter 7. If is Choquet <strong>in</strong>tegrable, we denote its<br />

<strong>in</strong>tegral by the symbol .<br />

We now <strong>in</strong>troduce the ipo <strong>in</strong>tegral, that is the symmetric Choquet <strong>in</strong>tegral, for extended realvalued<br />

functions with respect to <strong>Riesz</strong> space-valued capacities. We beg<strong>in</strong> with the follow<strong>in</strong>g:<br />

Def<strong>in</strong>itions 8.5 A measurable function is said to be simple if its range is f<strong>in</strong>ite.<br />

Let be the family of all f<strong>in</strong>ite subsets of which conta<strong>in</strong> zero. Given and , set<br />

and<br />

Let now , , where<br />

153, set<br />

where<br />

, and let be a measurable function. As <strong>in</strong> [204], p.<br />

If is an -valued capacity, we def<strong>in</strong>e the <strong>in</strong>tegral sum (with respect to<br />

(8.1)<br />

(8.2)<br />

) associated to and<br />

as follows:<br />

(where the ’s and the ’s are as <strong>in</strong> (8.1) and (8.2) respectively) if the right-hand side expression<br />

conta<strong>in</strong>s no expression of the type + ; moreover, we put by convention . We note<br />

that the set is directed. We say that (not necessarily positive) is ipo <strong>in</strong>tegrable<br />

( -<strong>in</strong>tegrable ) if there exists <strong>in</strong> the limit<br />

and <strong>in</strong> this case we denote the limit <strong>in</strong> (8.3) by the symbol<br />

, we say that<br />

. If the limit <strong>in</strong> (8.3) is or<br />

(8.3)


134 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 134-165<br />

9 (SL)-<strong>in</strong>tegral<br />

Abstract: In this chapter we deal with the strong Luz<strong>in</strong> ((SL)-) <strong>in</strong>tegral, related with the existence of primitives of<br />

functions <strong>in</strong> the weak sense. This <strong>in</strong>tegral is a variant of the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral, which co<strong>in</strong>cides with it <strong>in</strong> the<br />

real case, but is <strong>in</strong> general slightly different <strong>in</strong> the context of <strong>Riesz</strong> <strong>spaces</strong>, because some pathologies can occur.<br />

We also prove some versions of Hake and monotone convergence type theorems and of the Fundamental Theorem of<br />

Calculus, together with the basic properties.<br />

9.1 Ma<strong>in</strong> Properties <strong>in</strong> the Real and <strong>Riesz</strong> Space Context<br />

There are several generalizations of the Riemann <strong>in</strong>tegral, both <strong>in</strong> the classical and <strong>in</strong> abstract<br />

theory of <strong>in</strong>tegration. A variant of the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral, which co<strong>in</strong>cides with it for realvalued<br />

functions, but <strong>in</strong> general is different for <strong>Riesz</strong> space-valued mapp<strong>in</strong>gs, is the - (strong<br />

Luz<strong>in</strong>) <strong>in</strong>tegral, which was <strong>in</strong>vestigated <strong>in</strong> the case of real-valued functions by P. Y. Lee and R.<br />

Vborn (see [169,170]). The idea related with this type of <strong>in</strong>tegral is the follow<strong>in</strong>g: we <strong>in</strong>troduce a<br />

condition, so called strong Luz<strong>in</strong> condition or property , which lies strictly between absolute<br />

cont<strong>in</strong>uity and condition (roughly speak<strong>in</strong>g, we say that a function satisfies condition if it<br />

maps sets of measure zero onto sets of measure zero). We will say that a function is -<br />

<strong>in</strong>tegrable if it "admits" a "weak primitive" of class . In the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegration,<br />

condition will play, <strong>in</strong> the case of real-valued function, a role very similar to the one played<br />

by absolute cont<strong>in</strong>uity <strong>in</strong> the theory of the Lebesgue <strong>in</strong>tegral. Moreover, we will see that, for realvalued<br />

functions, the - and the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral will co<strong>in</strong>cide: this, <strong>in</strong> general, is<br />

true only <strong>in</strong> some particular <strong>Riesz</strong> <strong>spaces</strong>.<br />

We beg<strong>in</strong> with the real case. Sometimes, we will not report the proofs <strong>in</strong> this context because we<br />

will give them <strong>in</strong> the more sophisticated case of <strong>Riesz</strong> space-valued functions, which obviously<br />

<strong>in</strong>cludes the real sett<strong>in</strong>g as a particular case.<br />

Def<strong>in</strong>itions 9.1 Given an <strong>in</strong>terval we call division of any f<strong>in</strong>ite set<br />

, where x and for all . We denote by the<br />

class of all divisions of<br />

We call partition of a set of the type , where ,<br />

is a division and for all . A partition is said to be special if is an<br />

endpo<strong>in</strong>t of for every . We call mesh of a partition the quantity<br />

. Moreover, as no confusion can arise, given a measurable subset of the<br />

(extended) real l<strong>in</strong>e, we denote by its Lebesgue measure (f<strong>in</strong>ite or ).<br />

Def<strong>in</strong>ition 9.2 A decomposition of is a set of the type<br />

where is a family of pairwise nonoverlapp<strong>in</strong>g <strong>in</strong>tervals of and<br />

(9.1)<br />

for all .<br />

We note that a decomposition of is not necessarily a partition of .<br />

From now on, let us denote by the set of all positive real-valued functions, def<strong>in</strong>ed on an <strong>in</strong>terval<br />

.<br />

Def<strong>in</strong>ition 9.3 Given a partition or decomposition of and a<br />

function , we say that is -f<strong>in</strong>e if for all .<br />

Antonio Boccuto / Beloslav Riean / Marta Vrábelová<br />

All rights reserved - © 2009 <strong>Bentham</strong> <strong>Science</strong> Publishers Ltd.


(SL)-<strong>Integral</strong> <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 135<br />

Moreover, if is a mapp<strong>in</strong>g, and is a partition or decomposition as above, we<br />

denote by the quantity<br />

Def<strong>in</strong>ition 9.4 A function<br />

Lebesgue measure zero.<br />

is called gage if the set has<br />

We now endow the set of all gages with the follow<strong>in</strong>g order<strong>in</strong>g. Given two gages and , we say<br />

that if and only if for all .<br />

Def<strong>in</strong>ition 9.5 If is a gage, we say that a decomposition is -f<strong>in</strong>e if<br />

<br />

and for all .<br />

Remark 9.6 We note that there exist some gages , without -f<strong>in</strong>e partitions. However for all<br />

gages there exists a -f<strong>in</strong>e decomposition (for a proof, see [212], Teorema 1, p. 259).<br />

Def<strong>in</strong>ition 9.7 Let , and . We say that a function is of class<br />

or has property on if for every set of Lebesgue measure zero and<br />

there exists a map such that for any -f<strong>in</strong>e decomposition<br />

of , with and , we have:<br />

We say that is of class if it is of class on .<br />

The follow<strong>in</strong>g properties hold:<br />

Proposition 9.8<br />

1) The functions satisfy<strong>in</strong>g property form a l<strong>in</strong>ear space.<br />

2) Property implies cont<strong>in</strong>uity.<br />

3) If , , are such that is of class on each , then is of class also on<br />

.<br />

Def<strong>in</strong>ition 9.9 Let be the set of all gages, def<strong>in</strong>ed on . We say that is<br />

-<strong>in</strong>tegrable on if there exists a function of class such that, for every<br />

, there exists such that<br />

whenever is a -f<strong>in</strong>e decomposition of .<br />

The function will be called weak primitive of .<br />

In this case we put (by def<strong>in</strong>ition ) .<br />

The <strong>in</strong>tegral is well-def<strong>in</strong>ed: <strong>in</strong>deed we have the follow<strong>in</strong>g:<br />

(9.2)<br />

(9.3)


136 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riean, M. Vrábelová<br />

Proposition 9.10 Let be a set of Lebesgue measure zero, such that<br />

<br />

.<br />

for all and be a constant function. Then is a weak primitive of<br />

Proposition 9.11 Let<br />

is constant.<br />

and be as <strong>in</strong> Proposition 9.10, and be a weak primitive of . Then<br />

The follow<strong>in</strong>g fundamental result holds:<br />

Theorem 9.12 A function is <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegrable on if and only if it<br />

is -<strong>in</strong>tegrable on , and <strong>in</strong> this case we have<br />

Proof: We beg<strong>in</strong> with the "only if" part (see also [169]). S<strong>in</strong>ce is -<strong>in</strong>tegrable on ,<br />

then it is -<strong>in</strong>tegrable even on every sub<strong>in</strong>terval of . Let and<br />

The assertion follows because (9.3) holds when is replaced by and s<strong>in</strong>ce is of class<br />

on . The last fact follows s<strong>in</strong>ce is of class on<br />

for each : this is a consequence of the <strong>in</strong>equality<br />

which holds for every decomposition of : <strong>in</strong>deed, we note that,<br />

for sufficiently f<strong>in</strong>e decompositions, the quantity<br />

is sufficiently small, because is fixed, is bounded on and the <strong>in</strong>volved ’s belong to a<br />

fixed set of Lebesgue measure zero.<br />

We now turn to the "if" part (see also [169] and [170], pp. 169-170). Let be -<br />

<strong>in</strong>tegrable, let be a weak primitive of , and choose arbitrarily . There exists a<br />

gage such that<br />

for every -f<strong>in</strong>e decomposition of . Let be the set of the<br />

zeros of , and let . We note that is zero almost everywhere, and hence is<br />

<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegrable on , and


166 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 166-177<br />

10 Pettis-type Approach<br />

Abstract: In this chapter we beg<strong>in</strong> with <strong>in</strong>vestigat<strong>in</strong>g the Pettis, Bochner, Gelfand, Dunford, McShane and <strong>Kurzweil</strong>-<br />

<strong>Henstock</strong> <strong>in</strong>tegrals <strong>in</strong> the context of Banach <strong>spaces</strong>, and give some comparison results.<br />

Furthermore, we <strong>in</strong>troduce the Pettis-<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral for <strong>Riesz</strong> space-valued functions, giv<strong>in</strong>g a Hake-type<br />

convergence theorem and a version of the Levi monotone convergence theorem.<br />

<br />

10.1 Banach space Valued Case<br />

In this paragraph we will deal <strong>in</strong> short with the ma<strong>in</strong> elementary properties of the Pettis <strong>in</strong>tegral for<br />

Banach space-valued functions. We essentially follow [197], [196], [131] and [134].<br />

Let be a measure space. We say that is complete if every subset of any set<br />

with belongs to . Let be a Banach space, be its topological dual and<br />

be a f<strong>in</strong>ite complete measure space. We denote by the -ideal of all sets of<br />

measure zero.<br />

Def<strong>in</strong>ition 10.1 A function is said to be -measurable if there exists a sequence of<br />

simple functions such that<br />

for almost all (with respect to ).<br />

The follow<strong>in</strong>g characterization of -measurability holds (see [75], Corollary 3, p. 42):<br />

Proposition 10.2 A function is -measurable if and only if is the -almost<br />

everywhere uniform limit of a sequence of countably valued -measurable functions.<br />

Def<strong>in</strong>ition 10.3 We say that is scalarly -measurable if is -measurable for<br />

each .<br />

A map is said to be weak* scalarly -measurable if is -measurable for<br />

each .<br />

The follow<strong>in</strong>g result holds (Pettis’ measurability theorem):<br />

Theorem 10.4 A function is -measurable if and only if it is scalarly -measurable<br />

and there exists a set such that is a separable subset of .<br />

We say that is scalarly -bounded if there exists a positive real number such that<br />

Antonio Boccuto / Beloslav Riean / Marta Vrábelová<br />

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Pettis-Type Approach <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 167<br />

for almost all and for each . A map is said to be weak* scalarly -<br />

bounded if there exists a positive real number such that<br />

for almost all and for each . We say that is -bounded if there exists a<br />

positive real number such that<br />

for almost all .<br />

Proposition 10.5 If is -measurable and scalarly -bounded, then is -bounded.<br />

We now turn to the Pettis <strong>in</strong>tegral.<br />

Def<strong>in</strong>ition 10.6 A function is said to be scalarly -<strong>in</strong>tegrable if<br />

<br />

for each .<br />

A map is said to be weak* scalarly -<strong>in</strong>tegrable if for each .<br />

Def<strong>in</strong>ition 10.7 If<br />

by sett<strong>in</strong>g<br />

is scalarly -<strong>in</strong>tegrable, then we def<strong>in</strong>e the operator<br />

Def<strong>in</strong>ition 10.8 A scalarly -<strong>in</strong>tegrable function is said to be Pettis -<strong>in</strong>tegrable if<br />

for every there exists such that<br />

The set function is called the <strong>in</strong>def<strong>in</strong>ite Pettis <strong>in</strong>tegral of with respect to .<br />

A weak* scalarly -<strong>in</strong>tegrable function is said to be Gelfand -<strong>in</strong>tegrable if for<br />

every there exists such that<br />

The Gelfand <strong>in</strong>tegral of will be denoted by . If is considered as a -valued<br />

function, then its Gelfand <strong>in</strong>tegral <strong>in</strong> is called the Dunford <strong>in</strong>tegral and is denoted by<br />

.<br />

The follow<strong>in</strong>g results hold:<br />

Proposition 10.9 Every scalarly -<strong>in</strong>tegrable function is Dunford -<strong>in</strong>tegrable.<br />

Proposition 10.10 Every weak* scalarly -<strong>in</strong>tegrable function is Gelfand -<br />

<strong>in</strong>tegrable.


168 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riean, M. Vrábelová<br />

If is reflexive, then the Dunford and Pettis <strong>in</strong>tegrals co<strong>in</strong>cide. When is not reflexive, this, <strong>in</strong><br />

general, is not true (see [197]). However, the follow<strong>in</strong>g result holds:<br />

Proposition 10.11 If is a separable Banach space without an isomorphic copy of , then every<br />

Dunford <strong>in</strong>tegrable function is Pettis <strong>in</strong>tegrable.<br />

We now state some characterizations of Pettis <strong>in</strong>tegrability.<br />

Proposition 10.12 A scalarly -<strong>in</strong>tegrable function is Pettis -<strong>in</strong>tegrable if and only<br />

if the set<br />

is closed with respect to the weak* topology.<br />

Proposition 10.13 If<br />

weakly compact and the set<br />

is Pettis <strong>in</strong>tegrable, then the operator def<strong>in</strong>ed <strong>in</strong> 10.7 is<br />

is weakly closed <strong>in</strong> .<br />

We now state some convergence theorems for the Pettis <strong>in</strong>tegral <strong>in</strong> the context of Banach <strong>spaces</strong><br />

(for the proofs, see also [197], pp. 550-552 and [196], pp. 221-223). We beg<strong>in</strong> with the follow<strong>in</strong>g:<br />

Proposition 10.14 Let be any Banach space. A bounded set is relatively weakly<br />

compact if and only if, for every two sequences <strong>in</strong> and <strong>in</strong> the unit ball of , one<br />

has<br />

provided that all the <strong>in</strong>volved limits exist.<br />

Now we formulate the follow<strong>in</strong>g Vitali-type theorem:<br />

Theorem 10.15 Let be a map, and be a sequence of Pettis -<br />

<strong>in</strong>tegrable functions, such that <strong>in</strong> -measure for every , and the set<br />

is uniformly -<strong>in</strong>tegrable, that is, , such that<br />

<br />

, with and with .<br />

Then is Pettis -<strong>in</strong>tegrable, and


178 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 178-186<br />

11 Applications <strong>in</strong> Multivalued Logic<br />

Abstract: This chapter conta<strong>in</strong>s an <strong>in</strong>troduction to the theory of MV-algebras and states, together with the notion of<br />

observable.<br />

It is proved that every probability MV-algebra is weakly -distributive and some applications to <strong>in</strong>tuitionistic fuzzy sets<br />

(IF-sets) are given.<br />

Furthermore we show that the probability theory of IF-sets can be considered as a particular case of the probability<br />

theory on a suitable MV-algebra.<br />

<br />

11.1 MV-algebras<br />

While <strong>in</strong> the classical two-valued logic any assertion can be evaluated by two numbers , <strong>in</strong><br />

multivalued logic there is used the whole <strong>in</strong>terval . The disjunction, conjunction are considered<br />

as b<strong>in</strong>ary operations on and negation as a unary operation. These operations have been<br />

<strong>in</strong>troduced by ukasiewicz.<br />

Def<strong>in</strong>ition 11.1 If , then we def<strong>in</strong>e<br />

If , then actually corresponds to the disjunction, to the conjunction and<br />

to the negation. Moreover, if are subsets of a set , and , then<br />

The unit <strong>in</strong>terval with the ukasiewicz connectives and two fixed elements is<br />

a prototype of the notion of MV-algebra.<br />

Def<strong>in</strong>ition 11.2 An MV-algebra is a system satisfy<strong>in</strong>g the follow<strong>in</strong>g conditions:<br />

(i) is a commutative and associative b<strong>in</strong>ary operation;<br />

(ii) ;<br />

(iii) for any ;<br />

(iv) for any ;<br />

(v) for any .<br />

Antonio Boccuto / Beloslav Riean / Marta Vrábelová<br />

All rights reserved - © 2009 <strong>Bentham</strong> <strong>Science</strong> Publishers Ltd.


Applications <strong>in</strong> Multivalued Logic <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 179<br />

The properties (i) - (iv) are natural, the property (v) is sophisticated, of course, <strong>in</strong> the example of<br />

characteristic functions it means that<br />

where the symbols , mean the complement of the <strong>in</strong>volved sets , , and hence<br />

In general, the property (v) makes possible to def<strong>in</strong>e a partial order<strong>in</strong>g on . If we want to have<br />

, i.e. equals , then the equality will<br />

characterize the relation .<br />

Def<strong>in</strong>ition 11.3 We def<strong>in</strong>e , if .<br />

Proposition 11.4 The relation is a partial order<strong>in</strong>g, is a distributive lattice with the least<br />

element and the greatest element .<br />

Proof: See [64], Chapters 1, 3, and Lemma 6.6.4. <br />

Def<strong>in</strong>ition 11.5 An MV-algebra is said to be -complete or -MV-algebra if its underly<strong>in</strong>g<br />

lattice is -complete, i.e. every non-empty countable subset of has a supremum <strong>in</strong> .<br />

Analogously we can give the def<strong>in</strong>ition of -complete -group.<br />

We say that a lattice (or MV-algebra, or -group) is weakly -complete if it can be expressed as<br />

the union of -complete lattices (MV-algebras, -groups respectively).<br />

Example 11.6 Consider a family of functions satisfy<strong>in</strong>g the follow<strong>in</strong>g properties:<br />

<br />

(i)<br />

(ii) if , then<br />

(iii) if , then ;<br />

(iv) if , then .<br />

Then is an example of a -complete MV-algebra.<br />

A very important example of an MV-algebra is the MV-algebra <strong>in</strong>duced by an -group. Recall<br />

(see Chapter 2) that an -group (lattice ordered group) is a structure , where<br />

(i) is an Abelian group;<br />

(ii) is a lattice;<br />

(iii) if , then , .<br />

Example 11.7 Let be an -group, be its neutral element (i.e. for any ), be<br />

an element of such that . Put and def<strong>in</strong>e the follow<strong>in</strong>g<br />

operations on :


180 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riean, M. Vrábelová<br />

Then is an MV-algebra. We shall denote it by .<br />

Theorem 11.8 (Mundici) Every MV-algebra , up to isomorphisms, can be identified with the<br />

unit <strong>in</strong>terval of a unique -group with a strong unit (i.e. to any there exists a<br />

natural number such that ).<br />

Proof: See [64], Chapter 7 and [193]. <br />

The Mundici theorem stated above has some practical consequences because one can use group<br />

operations <strong>in</strong>stead of quite complicated axioms. Moreover, many known results of the theory of -<br />

groups can be used <strong>in</strong> the MV-algebra theory. We shall illustrate the advantage of the approach on<br />

the notion of state.<br />

Def<strong>in</strong>ition 11.9 Let be a -complete MV-algebra. A state is a map satisfy<strong>in</strong>g<br />

the follow<strong>in</strong>g conditions:<br />

<br />

(i) ;<br />

(ii) whenever and , it follows that ;<br />

(iii) if , then .<br />

Proposition 11.10 A map is a state if and only if it satisfies (i), (iii), and<br />

(ii’) if , then .<br />

Proof:<br />

If , then<br />

s<strong>in</strong>ce , hence . Moreover<br />

hence<br />

If , then , hence . Put . Then<br />

Of course,<br />

hence


<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 187-197 187<br />

12 Applications <strong>in</strong> Probability Theory<br />

Abstract: In this chapter we <strong>in</strong>troduce the concept of <strong>in</strong>dependence of states, and give a version of the weak law of<br />

large numbers. Moreover, we deal with conditional expectation <strong>in</strong> the context of <strong>Riesz</strong> <strong>spaces</strong>, and give three<br />

constructions.<br />

F<strong>in</strong>ally we present further results about probability theory <strong>in</strong> the context of IF-sets and <strong>in</strong> particular we deal with jo<strong>in</strong>t<br />

observables.<br />

12.1 Independence<br />

Recall (see Chapter 11) that a state (= probability measure) on an MV-algebra is a mapp<strong>in</strong>g<br />

such that<br />

;<br />

, whenever ;<br />

, whenever .<br />

Let be as <strong>in</strong> Chapter 11. A mapp<strong>in</strong>g is an observable, if<br />

;<br />

, and , whenever ;<br />

, whenever .<br />

It is easy to see that the composite map is a probability measure for any<br />

state and any observable . If is a random variable on a probability space ,<br />

then its probability distribution is def<strong>in</strong>ed by the formula<br />

Hence, if we def<strong>in</strong>e an observable on<br />

by the formula<br />

and a state by the formula<br />

<br />

then can be presented <strong>in</strong> the form<br />

Antonio Boccuto / Beloslav Riean / Marta Vrábelová<br />

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188 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riean, M. Vrábelová<br />

We see that corresponds with the notion of the probability distribution. Therefore the follow<strong>in</strong>g<br />

def<strong>in</strong>ition is natural.<br />

Def<strong>in</strong>ition 12.1 An observable is called <strong>in</strong>tegrable if there exists the <strong>in</strong>tegral<br />

The quantity is called the expectation of .<br />

<br />

We shall be <strong>in</strong>terested <strong>in</strong> a sequence of <strong>in</strong>dependent observables.<br />

Def<strong>in</strong>ition 12.2 Let be an MV-algebra, a state. We say that the observables<br />

are <strong>in</strong>dependent (with respect to ) if there exists an -dimensional<br />

observable such that<br />

for any . The mapp<strong>in</strong>g is called the jo<strong>in</strong>t observable of .<br />

Example 12.3 Consider a probability space and a sequence of <strong>in</strong>dependent random<br />

variables . The <strong>in</strong>dependence means that<br />

for any . Put . Then<br />

Put furthermore<br />

Then the <strong>in</strong>dependence of can be expressed by the formula<br />

,


Applications <strong>in</strong> Probability Theory <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 189<br />

Indeed,<br />

The mapp<strong>in</strong>g makes possible to def<strong>in</strong>e some functions of .<br />

Def<strong>in</strong>ition 12.4 Let be a Borel measurable function, be<br />

<strong>in</strong>dependent observables. The mapp<strong>in</strong>g is def<strong>in</strong>ed by the formula<br />

where is the jo<strong>in</strong>t observable of .<br />

Example 12.5 Let ( be a probability space, be observables,<br />

hence<br />

and aga<strong>in</strong> (putt<strong>in</strong>g<br />

<br />

. Then<br />

We see that the observable actually corresponds with the random variable<br />

If we put<br />

then we obta<strong>in</strong> the observable


198 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 198-212<br />

13 Integration <strong>in</strong> Metric Semigroups<br />

Abstract: In this chapter we present a <strong>Kurzweil</strong>-<strong>Henstock</strong>-type <strong>in</strong>tegral for metric semigroup-valued functions, def<strong>in</strong>ed<br />

on (possibly unbounded) sub<strong>in</strong>tervals of the extended real l<strong>in</strong>e. An example of a metric semigroup which is not a group<br />

is the set of all fuzzy numbers.<br />

Besides the elementary properties we prove a version of the <strong>Henstock</strong> lemma and some convergence theorems <strong>in</strong> this<br />

sett<strong>in</strong>g.<br />

13.1 Elementary Properties<br />

Although the book is devoted to measure and <strong>in</strong>tegration theory on ordered <strong>spaces</strong>, this chapter<br />

conta<strong>in</strong>s some result concern<strong>in</strong>g structures without order<strong>in</strong>g. More precisely, it deals with <strong>Kurzweil</strong>-<br />

<strong>Henstock</strong> <strong>in</strong>tegration for functions, def<strong>in</strong>ed on a (not necessarily bounded) <strong>in</strong>terval of the<br />

extended real l<strong>in</strong>e and with values <strong>in</strong> a metric semigroup. The basic example is the set of all<br />

fuzzy numbers. The idea of <strong>in</strong>vestigat<strong>in</strong>g <strong>in</strong>tegration <strong>in</strong> the context of metric semigroups arises from<br />

two papers of M. Matloka ([185, 186]; see also [218]).<br />

The <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral for functions def<strong>in</strong>ed <strong>in</strong> unbounded <strong>in</strong>tervals was <strong>in</strong>troduced<br />

and <strong>in</strong>vestigated <strong>in</strong> [36] for Banach space-valued maps and <strong>in</strong> [26] for <strong>Riesz</strong> space-valued mapp<strong>in</strong>gs<br />

(for real-valued functions, see [170]). In [282, 283] the "classical" <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral for<br />

-valued maps was studied (see also [139, 140, 141, 153, 163, 198, 281, 284, 285, 286]).<br />

In this chapter some basic properties of the -<strong>in</strong>tegral for metric semigroup-valued functions<br />

def<strong>in</strong>ed <strong>in</strong> (possibly unbounded) sub<strong>in</strong>tervals of the extended real l<strong>in</strong>e are <strong>in</strong>vestigated, and some<br />

convergence theorems are proved (see [28]).<br />

Def<strong>in</strong>ition 13.1 A metric semigroup is a structure , where ,<br />

, satisfy the follow<strong>in</strong>g conditions:<br />

(i) is a complete metric space;<br />

(ii) is a commutative semigroup endowed with a neutral element ;<br />

(iii) for any ;<br />

(iv) for all and ;<br />

(v) for each , ;<br />

(vi) for every , , and for each .<br />

A metric semigroup is called <strong>in</strong>variant, if for any .<br />

Observe that a consequence of <strong>in</strong>variance and the triangular property is the follow<strong>in</strong>g condition:<br />

(vii) whenever .<br />

An example of metric semigroup is the set of all fuzzy numbers (see also [28, 282]).<br />

Antonio Boccuto / Beloslav Riean / Marta Vrábelová<br />

All rights reserved - © 2009 <strong>Bentham</strong> <strong>Science</strong> Publishers Ltd.


Integration <strong>in</strong> Metric Semigroups <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 199<br />

Def<strong>in</strong>ition 13.2 A fuzzy number or fuzzy set is a function satisfy<strong>in</strong>g the follow<strong>in</strong>g<br />

conditions:<br />

<br />

(j) there exists such that ;<br />

(jj) the -cut set is convex for ;<br />

(jjj) is upper semi-cont<strong>in</strong>uous, i.e. any -cut is a closed subset of ;<br />

(jv) the support of the function is a compact set.<br />

Any real number can be identified with a fuzzy number <strong>in</strong> the follow<strong>in</strong>g way:<br />

i.e. , and , if .<br />

The set of all fuzzy numbers is denoted by .<br />

We now endow with a metric and a l<strong>in</strong>ear structure (see also [28, 282]). We def<strong>in</strong>e the<br />

Hausdorff distance on the set of all compact possibly degenerate <strong>in</strong>tervals <strong>in</strong> :<br />

Let . It is easy to check that, for every , there exist , , , (depend<strong>in</strong>g<br />

on ) such that , . So, for , set<br />

Us<strong>in</strong>g this def<strong>in</strong>ition becomes a complete metric space.<br />

To def<strong>in</strong>e a l<strong>in</strong>ear structure on , recall that every fuzzy number is completely determ<strong>in</strong>ed by<br />

its -cuts. Hence, for any , and , set<br />

(here, ).<br />

F<strong>in</strong>ally, we note that is not a group, but only a semigroup (see also [28]), <strong>in</strong> fact let<br />

be def<strong>in</strong>ed by the formula:<br />

Then is given by


200 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riean, M. Vrábelová<br />

Note that is not the zero element , but<br />

On the other hand the subset consist<strong>in</strong>g of all functions , , is group<br />

isomorphic to the commutative group . There are many applications of the space <strong>in</strong> the<br />

fuzzy set theory. Let us mention an application from the probability theory.<br />

A random variable is a measurable map from the probability space to , a fuzzy random<br />

variable is a measurable mapp<strong>in</strong>g from the probability space to . S<strong>in</strong>ce expectation<br />

<strong>in</strong> any probability model of the Kolmogorov type co<strong>in</strong>cides with an abstract <strong>in</strong>tegral of the<br />

Lebesgue type, the theory of the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral with values <strong>in</strong> could be useful <strong>in</strong><br />

the theory of fuzzy random variables. Moreover, the axiomatic approach presented <strong>in</strong> Def<strong>in</strong>ition<br />

13.1 could be simpler for exposition and possibly useful for applications.<br />

Of course, every random variable with values <strong>in</strong> a Banach space is also a special k<strong>in</strong>d of function<br />

with values <strong>in</strong> a metric semigroup.<br />

We now <strong>in</strong>troduce the <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral for functions with values <strong>in</strong> a metric<br />

semigroup . From now on, we denote by a closed <strong>in</strong>terval or halfl<strong>in</strong>e conta<strong>in</strong>ed <strong>in</strong> , or<br />

the whole of . Moreover, given a measurable set , we denote by its Lebesgue measure<br />

(this quantity can be f<strong>in</strong>ite or . Our <strong>in</strong>tegral deals with -valued functions def<strong>in</strong>ed on ,<br />

but it can be <strong>in</strong>vestigated analogously if we take functions def<strong>in</strong>ed on or on halfl<strong>in</strong>es of the type<br />

or , with . The concepts of partition, decomposition, gauge, -, -f<strong>in</strong>eness<br />

and Riemann sum are as the ones formulated <strong>in</strong> Chapter 7.<br />

We now formulate our def<strong>in</strong>ition of <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral for functions def<strong>in</strong>ed on and<br />

with values <strong>in</strong> a metric semigroup .<br />

Def<strong>in</strong>ition 13.3 We say that a function is <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegrable (<strong>in</strong> short<br />

-<strong>in</strong>tegrable or simply <strong>in</strong>tegrable ) on if there exists an element such that<br />

there exist a function and a positive real number such that<br />

<br />

(13.1)<br />

whenever is a -f<strong>in</strong>e partition of any bounded <strong>in</strong>terval with<br />

and . In this case we say that is the -<strong>in</strong>tegral of , and<br />

we denote the element by the symbol .


<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 213-223 213<br />

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214 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riean, M. Vrábelová<br />

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d’ensemble”, Ann. Scuola Sup. Pisa, vol. 33, pp. 61-99, 1977.<br />

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75-87, 1986.<br />

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Symposium 2003, pp. 87-91, 2003.<br />

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555, 2003/2004.


224 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces, 224-226<br />

absolutely cont<strong>in</strong>uous function ............................ 119,140<br />

additive ..................................................................... 62,71<br />

algebra............................................................................ 72<br />

Archimedean l-group ..................................................... 27<br />

asymmetric <strong>in</strong>tegral ..................................................... 126<br />

Banach space .......................................................... 99,166<br />

Bochner <strong>in</strong>tegral .......................................................... 169<br />

Bolzano-Cauchy condition ......... 7,45,64,89,107,145,202<br />

canonical embedd<strong>in</strong>g ..................................................... 37<br />

capacity<br />

cont<strong>in</strong>uous ............................................................... 112<br />

subadditive .............................................................. 112<br />

submodular ............................................................. 112<br />

Cauchy .................................. 7,33,45,64,89,107,145,202<br />

Choquet <strong>in</strong>tegral ...................................................113,126<br />

comonotonic ................................................................ 112<br />

complete measure ........................................................ 166<br />

compound partition........................................................ 59<br />

conditional expectation ................................ 128,192,194<br />

conditional probability ................................................ 191<br />

cont<strong>in</strong>uity<br />

of the <strong>in</strong>tegral ....................................................... 9,153<br />

convergence<br />

dom<strong>in</strong>ated theorem .................................... 80,124,169<br />

monotone theorem .................... 20,66,77,123,124,176<br />

uniform ..................................................................... 48<br />

uniformtheorem .......................................... 18,48,211<br />

Cous<strong>in</strong>'s lemma .................................................... 3,90,135<br />

cuts<br />

α-cuts ...................................................................... 199<br />

(D)-Cauchy .................................................................... 33<br />

(D)-complete .................................................................. 33<br />

(D)-convergence ............................................................ 27<br />

(D)-sequence .................................................................. 27<br />

decomposition ................................................... 84,96,134<br />

Dedek<strong>in</strong>d complete lattice ............................................. 25<br />

differentiable function ................................................. 141<br />

distance<br />

Hausdorff ................................................................ 199<br />

distribution function .................................................... 127<br />

division ........................................................ 1,52,134,170<br />

dom<strong>in</strong>ated convergence theorem ................... 80,124,169<br />

double <strong>in</strong>tegral ............................................................... 52<br />

Dunford <strong>in</strong>tegral .......................................................... 167<br />

Egorov property ............................................................. 28<br />

equi<strong>in</strong>tegrable functions ....................................... 161,209<br />

INDEX<br />

Antonio Boccuto / Beloslav Riečan / Marta Vrábelová<br />

All rights reserved - © 2009 <strong>Bentham</strong> <strong>Science</strong> Publishers Ltd.<br />

evaluation map ......................................................... 37,39<br />

expectation ........................................................... 128,188<br />

conditional ................................................ 128,192,194<br />

faithful state ................................................................. 181<br />

Fatou lemma ................................................................ 120<br />

Freml<strong>in</strong> lemma ......................................................... 28,43<br />

Fub<strong>in</strong>i theorem .............................................................. 60<br />

function<br />

additive ................................................................ 62,71<br />

absolutely cont<strong>in</strong>uous ...................................... 119,140<br />

cont<strong>in</strong>uous .................................................... 43,56,140<br />

differentiable .......................................................... 141<br />

Lipschitzian ............................................................ 142<br />

measurable ....................................................... 112,166<br />

of bounded variation ......................................... 17,140<br />

regular .................................................................. 62,71<br />

scalarly bounded .................................................... 166<br />

scalarly <strong>in</strong>tegrable ................................................. 167<br />

scalarly measurable ............................................... 166<br />

(u)-cont<strong>in</strong>uous ........................................................ 141<br />

(u)-differentiable .................................................... 141<br />

uniformly cont<strong>in</strong>uous ............................................. 141<br />

weak* scalarly bounded ......................................... 163<br />

weak* scalarly <strong>in</strong>tegrable ...................................... 167<br />

weak* scalarly measurable .................................... 166<br />

functional<br />

l<strong>in</strong>ear ......................................................................... 37<br />

order bounded ........................................................... 37<br />

order cont<strong>in</strong>uous ....................................................... 37<br />

positive ..................................................................... 37<br />

Fundamental Theorem ........................................... 10,147<br />

fuzzy event <strong>in</strong>tuitionistic ...................................... 184,194<br />

fuzzy number ............................................................... 199<br />

fuzzy random variable ................................................. 200<br />

fuzzy set ....................................................................... 199<br />

fuzzy set <strong>in</strong>tuitionistic .......................................... 184,194<br />

gage.............................................................................. 135<br />

gauge ................................................................. 62,84,172<br />

Gelfand <strong>in</strong>tegral ........................................................... 167<br />

generalized McShane partition ................................... 172<br />

Hausdorff distance ...................................................... 199<br />

<strong>Henstock</strong> lemma .................................... 15,66,76,147,208<br />

improper <strong>in</strong>tegral ........................................................... 12<br />

<strong>in</strong>dependent observable ............................................... 188<br />

<strong>in</strong>fimum ......................................................................... 25<br />

<strong>in</strong>tegrable observable .................................................. 188<br />

<strong>in</strong>tegral<br />

asymmetric ............................................................ 126


Index <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces 225<br />

Bochner .................................................................. 169<br />

Choquet ........................................................... 113,126<br />

double ...................................................................... 52<br />

Dunford .................................................................. 167<br />

Gelfand .................................................................. 167<br />

improper .................................................................. 12<br />

<strong>Kurzweil</strong>-<strong>Henstock</strong> ............... 3,44,52,63,64,72,85,97,<br />

99,100,107,144,170<br />

<strong>Kurzweil</strong>-<strong>Henstock</strong> on unbounded <strong>in</strong>tervals ... 24,200<br />

<strong>Kurzweil</strong>-Stieltjes .................................................... 49<br />

Lebesgue ................................................................ 144<br />

McShane ......................................................... 170,172<br />

monotone ............................................................... 113<br />

p-<strong>in</strong>tegral ................................................................ 173<br />

Pettis ...................................................................... 167<br />

Riemann .............................................................. 2,143<br />

SL .................................................................... 135,155<br />

symmetric .............................................................. 113<br />

Šipoš ...................................................................... 113<br />

<strong>in</strong>tegration by parts ........................................................ 12<br />

<strong>in</strong>tuitionistic fuzzy event ...................................... 184,194<br />

<strong>in</strong>tuitionistic fuzzy set ..........................................184,194<br />

<strong>in</strong>variant metric semigroup ......................................... 198<br />

jo<strong>in</strong>t observable ........................................................... 188<br />

<strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>in</strong>tegral ................. 3,24,44,52,63,64,<br />

72,85,97,99,100,107,144,170,200<br />

<strong>Kurzweil</strong>-Stieltjes <strong>in</strong>tegral ............................................ 49<br />

l-group .................................................................... 26,179<br />

Archimedean ........................................................... 27<br />

Dedek<strong>in</strong>d complete .................................................. 27<br />

σ-complete ............................................................. 179<br />

weakly σ-complete ................................................ 179<br />

weakly σ -distributive .............................................. 29<br />

L-observable ......................................................... 185,195<br />

L-state .......................................................................... 185<br />

laterally complete lattice ............................................... 25<br />

lattice .............................................................................. 25<br />

Dedek<strong>in</strong>d complete ................................................... 25<br />

laterally complete ..................................................... 25<br />

super Dedek<strong>in</strong>d complete ......................................... 25<br />

universally complete ........................................... 25,40<br />

law of large numbers<br />

strong law ............................................................... 129<br />

weak law .......................................................... 131,189<br />

Lebesgue <strong>in</strong>tegral ....................................................... 144<br />

Lemma<br />

Cous<strong>in</strong> ............................................................. 3,90,135<br />

Fatou ....................................................................... 120<br />

Freml<strong>in</strong>................................................................. 28,43<br />

<strong>Henstock</strong> .......................................... 15,66,76,147,208<br />

l<strong>in</strong>ear functional ............................................................. 37<br />

l<strong>in</strong>ear operator ................................................................ 41<br />

locally determ<strong>in</strong>ed measure ......................................... 171<br />

Maeda-Ogasawara-Vulikh<br />

theorem .......................................................................... 40<br />

McShane <strong>in</strong>tegral ................................................. 170,172<br />

McShane partition ....................................................... 170<br />

mean ............................................................................ 112<br />

measurable function .................................................... 112<br />

measure ........................................................................ 112<br />

complete ................................................................. 166<br />

locally determ<strong>in</strong>ed .................................................. 171<br />

quasi-Radon ............................................................ 171<br />

Radon...................................................................... 171<br />

semif<strong>in</strong>ite ................................................................ 171<br />

metric semigroup ......................................................... 198<br />

<strong>in</strong>variant .................................................................. 198<br />

monotone convergence theorem ... 20,66,77,123,124,176<br />

monotone <strong>in</strong>tegral........................................................ 113<br />

Mundici theorem ......................................................... 180<br />

MV-algebra ................................................................. 178<br />

σ-complete ............................................................. 179<br />

σ-MV-algebra ........................................................ 179<br />

weakly σ-complete ................................................ 179<br />

weakly σ-distributive ............................................ 181<br />

MV-algebra with product ............................................ 192<br />

(O)-convergence .............................................. 27,111,138<br />

(O)-net ............................................................. 27,111,139<br />

(O)-sequence ................................................... 27,111,140<br />

observable ............................................................. 181,187<br />

<strong>in</strong>dependent ............................................................ 188<br />

<strong>in</strong>tegrable ................................................................ 188<br />

jo<strong>in</strong>t ......................................................................... 188<br />

L-observable .................................................... 185,195<br />

operator<br />

l<strong>in</strong>ear ......................................................................... 41<br />

p-<strong>in</strong>tegral ..................................................................... 173<br />

partially ordered set ....................................................... 25<br />

partition ...................................................... 62,96,134,173<br />

compound ................................................................. 59<br />

δ-f<strong>in</strong>e ............................................................ 1,2,52,134<br />

generalized McShane ............................................. 172<br />

McShane ................................................................. 170<br />

special .............................................................. 134,170<br />

perfect space .................................................................. 38<br />

Pettis <strong>in</strong>tegral ............................................................... 167<br />

primitive ........................................................................ 10<br />

weak ................................................................. 135,155<br />

probability<br />

conditional .............................................................. 191<br />

measure ................................................................... 187<br />

product ...................................................................... 40,72<br />

MV-algebra with .................................................... 192<br />

property<br />

Egorov ...................................................................... 28


226 <strong>Kurzweil</strong>-<strong>Henstock</strong> <strong>Integral</strong> <strong>in</strong> <strong>Riesz</strong> Spaces A. Boccuto, B. Riečan, M. Vrábelová<br />

property σ ............................................................. 103,139<br />

property SL .................................................................. 135<br />

quasi-Radon measure space ........................................ 171<br />

(r)-convergence............................................................ 138<br />

Radon measure space .................................................. 171<br />

random variable ..................................... 112,129,132,200<br />

fuzzy ....................................................................... 200<br />

regular ....................................................................... 62,71<br />

Riemann <strong>in</strong>tegral ...................................................... 2,143<br />

<strong>Riesz</strong> space .................................................................... 37<br />

super Dedek<strong>in</strong>d complete ....................................... 139<br />

scalarly bounded function ........................................... 166<br />

scalarly <strong>in</strong>tegrable function ......................................... 167<br />

scalarly measurable function ....................................... 166<br />

semif<strong>in</strong>ite measure ....................................................... 171<br />

semivariation<br />

bounded .................................................................... 50<br />

separat<strong>in</strong>g ....................................................................... 63<br />

set<br />

partially ordered ....................................................... 25<br />

SL class ........................................................................ 135<br />

SL <strong>in</strong>tegral ............................................................ 135,155<br />

SL property .................................................................. 135<br />

space<br />

+-space ...................................................................... 37<br />

π-space ...................................................................... 37<br />

ρ-space ...................................................................... 39<br />

Banach ............................................................... 99,166<br />

perfect ....................................................................... 38<br />

Stonian ...................................................................... 40<br />

special partition .................................................... 134,170<br />

state ...................................................................... 180,187<br />

faithful .................................................................... 181<br />

L-state ..................................................................... 185<br />

strong law of large numbers ........................................ 129<br />

submodular theorem .................................................... 125<br />

super Dedek<strong>in</strong>d complete lattice ................................... 25<br />

super Dedek<strong>in</strong>d complete <strong>Riesz</strong> space ........................ 139<br />

supremum ...................................................................... 25<br />

symmetric <strong>in</strong>tegral ....................................................... 113<br />

Šipoš <strong>in</strong>tegral ............................................................... 113<br />

theorem<br />

dom<strong>in</strong>ated convergence ............................. 80,124,169<br />

Fub<strong>in</strong>i ....................................................................... 60<br />

Maeda-Ogasawara-Vulikh ....................................... 40<br />

monotone convergence ............ 20,66,77,123,124,176<br />

Mundici .................................................................. 180<br />

submodular ............................................................. 125<br />

uniform convergence ................................... 18,48,211<br />

(u)-cont<strong>in</strong>uous function ............................................... 141<br />

(u)-differentiable function .......................................... 141<br />

uniform convergence ..................................................... 48<br />

uniform convergence theorem .......................... 18,48,211<br />

uniformly cont<strong>in</strong>uous function .................................... 141<br />

uniformly <strong>in</strong>tegrable functions ............................. 143,168<br />

universally complete lattice ..................................... 25,40<br />

variation<br />

bounded ............................................................. 17,140<br />

total ........................................................................... 17<br />

vector lattice .................................................................. 37<br />

weak law of large numbers .................................. 131,189<br />

weak primitive ...................................................... 135,155<br />

weak* scalarly bounded function ............................... 167<br />

weak* scalarly <strong>in</strong>tegrable function ............................. 167<br />

weak* scalarly measurable function ........................... 166<br />

weakly σ-complete l-group ......................................... 179<br />

weakly σ-complete MV-algebra ................................. 179<br />

weakly σ-distributive l-group ....................................... 29<br />

weakly σ-distributive MV-algebra ............................. 181

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