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GSOS for probabilistic transition systems (Extended Abstract)
, 2002
"... We introduce probabilistic GSOS, an operator specification format for (reactive) probabilistic transition systems which arises as an adaptation of the known GSOS format for labelled (nondeterministic) transition systems. Like the standard one, the format is well behaved in the sense that on all mode ..."
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We introduce probabilistic GSOS, an operator specification format for (reactive) probabilistic transition systems which arises as an adaptation of the known GSOS format for labelled (nondeterministic) transition systems. Like the standard one, the format is well behaved in the sense that on all models bisimilarity is a congruence and the uptocontext proof principle is valid. Moreover, every specification has a final model which can be shown to offer unique solutions for guarded recursive equations. The format covers operator specifications from the literature, so that the wellbehavedness results given for those arise as instances of our general one.
Talk II: Simple (Co)Induction Principles
, 2001
"... e Theorem 1.3 (Coiteration). For all f : C ! TC there exists a unique g : C ! X:TX such that C g ## f ## X:TX out ## TC Tg ## TX:TX commutes. Example 1.4 (Coiteration on Streams). Let TX = L X for some xed set L and denote the set of (innite) sequences over L by L N = ff j f : N ! L ..."
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e Theorem 1.3 (Coiteration). For all f : C ! TC there exists a unique g : C ! X:TX such that C g ## f ## X:TX out ## TC Tg ## TX:TX commutes. Example 1.4 (Coiteration on Streams). Let TX = L X for some xed set L and denote the set of (innite) sequences over L by L N = ff j f : N ! Lg. Then hhd; tli : L N ! L L N is nal, where hd(f) = f(0) and tl(f<F10.9
Generalized Coinduction
, 2003
"... this paper express that the above principles work under di#erent additional assumptions which are needed to show that the large system can actually be constructed inside the category. The basic Theorem requires the existence of countable coproducts. Later we also present a variant where the functor ..."
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this paper express that the above principles work under di#erent additional assumptions which are needed to show that the large system can actually be constructed inside the category. The basic Theorem requires the existence of countable coproducts. Later we also present a variant where the functor T comes a as a monad, the functor F is taken from a copointed functor, and the distributive law # is assumed to interact nicely with this additional structure (i.e. # should be a distributive law of the monad over the copointed functor, see again (Lenisa et al., 2000))
Stream Differential Equations: concrete formats for coinductive definitions
, 2011
"... In this article we give an accessible introduction to stream differential equations, ie., equations that take the shape of differential equations from analysis and that are used to define infinite streams. Furthermore we discuss a syntactic format for stream differential equations that ensures that ..."
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In this article we give an accessible introduction to stream differential equations, ie., equations that take the shape of differential equations from analysis and that are used to define infinite streams. Furthermore we discuss a syntactic format for stream differential equations that ensures that any system of equations that fits into the format has a unique solution. It turns out that the stream functions that can be defined using our format are precisely the causal stream functions. Finally, we are going to discuss nonstandard stream calculus that uses basic (co)operations different from the usual head and tail operations in order to define and to reason about streams and stream functions. 1
Submitted to ICFP’13 Unifying Recursion Schemes
"... Folds over inductive datatypes are well understood and widely used. In their plain form, they are quite restricted; but many disparate generalisations have been proposed that enjoy similar calculational benefits. There have also been attempts to unify the various generalisations: two prominent such ..."
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Folds over inductive datatypes are well understood and widely used. In their plain form, they are quite restricted; but many disparate generalisations have been proposed that enjoy similar calculational benefits. There have also been attempts to unify the various generalisations: two prominent such unifications are the ‘recursion schemes from comonads ’ of Uustalu, Vene and Pardo, and our own ‘adjoint folds’. Until now, these two unified schemes have appeared incompatible. We show that this appearance is illusory: in fact, adjoint folds subsume recursion schemes from comonads. The proof of this claim involves standard constructions in category theory that are nevertheless not well known in functional programming: EilenbergMoore categories and bialgebras. The link between the two schemes is provided by the fusion rule of categorical fixedpoint calculus.