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Mongruences and Cofree Coalgebras
 Algebraic Methods and Software Technology, number 936 in Lect. Notes Comp. Sci
, 1995
"... . A coalgebra is introduced here as a model of a certain signature consisting of a type X with various "destructor" function symbols, satisfying certain equations. These destructor function symbols are like methods and attributes in objectoriented programming: they provide access to the type (or st ..."
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Cited by 30 (10 self)
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. A coalgebra is introduced here as a model of a certain signature consisting of a type X with various "destructor" function symbols, satisfying certain equations. These destructor function symbols are like methods and attributes in objectoriented programming: they provide access to the type (or state) X. We show that the category of such coalgebras and structure preserving functions is comonadic over sets. Therefore we introduce the notion of a `mongruence' (predicate) on a coalgebra. It plays the dual role of a congrence (relation) on an algebra. An algebra is a set together with a number of operations on this set which tell how to form (derived) elements in this set, possibly satisfying some equations. A typical example is a monoid, given by a set M with operations 1 ! M , M \Theta M ! M . Here 1 = f;g is a singleton set. In mathematics one usually considers only singletyped algebras, but in computer science one more naturally uses manytyped algebras like 1 ! list(A), A \Theta l...
Finality Regained  A Coalgebraic Study of Scottsets and Multisets
 Arch. Math. Logic
, 1999
"... In this paper we study iterated circular multisets in a coalgebraic framework. We will produce two essentially different universes of suchsets. The unisets of the first universe will be shown to be precisely the sets of the Scott universe. The unisets of the second universe will be precisely the ..."
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Cited by 21 (1 self)
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In this paper we study iterated circular multisets in a coalgebraic framework. We will produce two essentially different universes of suchsets. The unisets of the first universe will be shown to be precisely the sets of the Scott universe. The unisets of the second universe will be precisely the sets of the AFAuniverse. Wewillhave a closer look into the connection of the iterated circular multisets and arbitrary trees. Key words: multiset, nonwellfounded set, Scottuniverse, AFA, coalgebra, modal logic, graded modalities MSC2000 codes: 03B45, 03E65, 03E70, 18A15, 18A22, 18B05, 68Q85 1 Contents 1 Introduction 3 1.1 Multisets on a Given Domain . . . . . . . . . . . . . . . . . . . . 3 1.2 Iterated and Circular Multisets . . . . . . . . . . . . . . . . . . . 6 1.3 Organization of the Paper . . . . . . . . . . . . . . . . . . . . . . 7 2 Prerequisites 8 2.1 Coalgebras and Morphisms . . . . . . . . . . . . . . . . . . . . . 8 2.1.1 A Prototype: Pow . . . . . . . . . . . . . . . ...
Final Universes of Processes
 PROC. MATH. FOUNDATIONS OF PROGRAMMING SEMANTICS. SPRINGER LECT. NOTES COMP. SCI. (802
, 1994
"... We describe the final universe approach to the characterisation of semantic universes and illustrate it by giving characterisations of the universes of CCS and CSP processes. ..."
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Cited by 19 (1 self)
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We describe the final universe approach to the characterisation of semantic universes and illustrate it by giving characterisations of the universes of CCS and CSP processes.
Generic trace semantics via coinduction
 Logical Methods in Comp. Sci
, 2007
"... Abstract. Trace semantics has been defined for various kinds of statebased systems, notably with different forms of branching such as nondeterminism vs. probability. In this paper we claim to identify one underlying mathematical structure behind these “trace ..."
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Cited by 17 (6 self)
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Abstract. Trace semantics has been defined for various kinds of statebased systems, notably with different forms of branching such as nondeterminism vs. probability. In this paper we claim to identify one underlying mathematical structure behind these “trace
Domain Equations for Probabilistic Processes
 In Proc. Express'97. Electronic Notes in Theoretical Computer Science 7
, 1997
"... ) Christel Baier Fakultat fur Mathematik & Informatik Universitat Mannheim 68131 Mannheim, Germany Marta Kwiatkowska 1 School of Computer Science University of Birmingham Edgbaston, Birmingham B15 2TT, UK Abstract In this paper we consider Milner's calculus CCS enriched by a probabilistic choice ..."
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Cited by 16 (1 self)
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) Christel Baier Fakultat fur Mathematik & Informatik Universitat Mannheim 68131 Mannheim, Germany Marta Kwiatkowska 1 School of Computer Science University of Birmingham Edgbaston, Birmingham B15 2TT, UK Abstract In this paper we consider Milner's calculus CCS enriched by a probabilistic choice operator. The calculus is given operational semantics based on probabilistic transition systems. We define operational notions of preorder and equivalence as probabilistic extensions of the simulation preorder and the bisimulation equivalence respectively. We extend existing categorytheoretic techniques for solving domain equations to the probabilistic case and give two denotational semantics for the calculus. The first, "smooth", semantic model arises as a solution of a domain equation involving the probabilistic powerdomain and solved in the category CONT? of continuous domains. The second model also involves appropriately restricted probabilistic powerdomain, but is constructed in the c...
Parametric Corecursion
 Theoretical Computer Science
"... This paper gives a treatment of substitution for "parametric" objects in final coalgebras, and also presents principles of definition by corecursion for such objects. The substitution results are coalgebraic versions of wellknown consequences of initiality, and the work on corecursion is a gener ..."
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Cited by 14 (3 self)
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This paper gives a treatment of substitution for "parametric" objects in final coalgebras, and also presents principles of definition by corecursion for such objects. The substitution results are coalgebraic versions of wellknown consequences of initiality, and the work on corecursion is a general formulation which allows one to specify elements of final coalgebras using systems of equations. One source of our results is the theory of hypersets, and at the end of this paper we sketch a development of that theory which calls upon the general work of this paper to a very large extent and particular facts of elementary set theory to a much smaller extent. 1 Introduction This paper has two overall goals. The first is a general theory of substitution and corecursion having to do with final coalgebras. To give an example of the kind of phenomena we have in mind, consider any set S and form the functor F on sets defined by Fa = S \Theta a \Theta a. F is defined on functions in the u...
On the Foundations of Corecursion
 Logic Journal of the IGPL
, 1997
"... We consider foundational questions related to the definition of functions by corecursion. This method is especially suited to functions into the greatest fixed point of some monotone operator, and it is most applicable in the context of nonwellfounded sets. We review the work on the Special Final C ..."
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Cited by 13 (1 self)
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We consider foundational questions related to the definition of functions by corecursion. This method is especially suited to functions into the greatest fixed point of some monotone operator, and it is most applicable in the context of nonwellfounded sets. We review the work on the Special Final Coalgebra Theorem of Aczel [1] and the Corecursion Theorem of Barwise and Moss [4]. We offer a condition weaker than Aczel's condition of uniformity on maps, and then we prove a result relating the operators satisfying the new condition to the smooth operators of [4]. Keywords: corecursion, coalgebra, operator on sets 1 Introduction By a stream of natural numbers we mean a pair hn; si where n 2 N and s is again a stream of natural numbers. Let f : N ! N . Consider the following function which purports to define a function from N into the streams: iter f (n) = hn; iter f f(n)i (1.1) For each n, iter f (n) is a stream, so iter f itself is a function from numbers to streams. This is an examp...
Invariants, Bisimulations and the Correctness of Coalgebraic Refinements
 Techn. Rep. CSIR9704, Comput. Sci. Inst., Univ. of Nijmegen
, 1997
"... . Coalgebraic specifications are used to formally describe the behaviour of classes in objectoriented languages. In this paper, a general notion of refinement between two such coalgebraic specifications is defined, capturing the idea that one "concrete" class specification realises the behaviour of ..."
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Cited by 12 (4 self)
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. Coalgebraic specifications are used to formally describe the behaviour of classes in objectoriented languages. In this paper, a general notion of refinement between two such coalgebraic specifications is defined, capturing the idea that one "concrete" class specification realises the behaviour of the other, "abstract" class specification. Two (complete) prooftechniques are given to establish such refinements: one involving an invariant (a predicate that is closed under transitions) on the concrete class, and one involving a bisimulation (a relation that is closed under transitions) between the concrete and the abstract class. The latter can only be used if the abstract class is what we call totally specified. Parts of the underlying theory of invariants and bisimulations in a coalgebraic setting are included, involving least and greatest invariants and connections between invariants and bisimulations. Also, the proofprinciples are illustrated in examples (which are fully formalise...