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Reactive Systems: Modelling, Specification and Verification - Cs.ioc.ee

Reactive Systems: Modelling, Specification and Verification - Cs.ioc.ee

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2.2. CCS, FORMALLY 31<br />

Exercise 2.8 Assume that A def<br />

= b.a.B. By using the SOS rules for CCS prove the<br />

existence of the following transitions:<br />

• (A | b.0) \ {b} τ → (a.B | 0) \ {b},<br />

• (A | b.a.B) + (b.A)[a/b] b → (A | a.B), <strong>and</strong><br />

• (A | b.a.B) + (b.A)[a/b] a → A[a/b].<br />

Exercise 2.9 Draw (part of) the transition graph for the process name A whose<br />

behaviour is given by the defining equation<br />

A def<br />

= (a.A) \ b .<br />

The resulting transition graph should have infinitely many states. Can you think of<br />

a CCS term that generates a finite labelled transition system that should intuitively<br />

have the same behaviour as A? <br />

Exercise 2.10 Draw (part of) the transition graph for the process name A whose<br />

behaviour is given by the defining equation<br />

A def<br />

= (a0.A)[f]<br />

where we assume that the set of channel names is {a0, a1, a2, . . .}, <strong>and</strong> f(ai) =<br />

ai+1 for each i.<br />

The resulting transition graph should (again!) have infinitely many states. Can<br />

you give an argument showing that there is no finite state labelled transition system<br />

that could intuitively have the same behaviour as A? <br />

Exercise 2.11<br />

1. Draw the transition graph for the process name Mutex1 whose behaviour is<br />

given by the defining equation<br />

Mutex1<br />

User<br />

def<br />

= (User | Sem) \ {p, v}<br />

def<br />

= ¯p.enter.exit.¯v.User<br />

Sem def<br />

= p.v.Sem .

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