Kurzweil-Henstock Integral in Riesz spaces - Bentham Science
Kurzweil-Henstock Integral in Riesz spaces - Bentham Science
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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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 />
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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 />
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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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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