Kidane Yemane - Academia.edu (original) (raw)
Papers by Kidane Yemane
Electronic Notes in Theoretical Computer Science, 2009
We consider a typed lambda-calculus with no function types, only alternating sum and product type... more We consider a typed lambda-calculus with no function types, only alternating sum and product types, so that closed terms represent strategies. We add nondeterminism and consider strategies up to lower (i.e. divergence-insensitive) bisimilarity. We investigate the question: when is a function on strategies definable by an open term (with sufficiently large nondeterminism)? The answer is: when it is "exploratory". This is a kind of iterated continuity property, coinductively defined, that is decidable in the case of a function between finite types. In particular, any exploratory function between countably nondeterministic strategies is definable by a continuum nondeterministic term.
Electronic Notes in Theoretical Computer Science, 2004
We apply the recently developed techniques of higher order abstract syntax and functorial operati... more We apply the recently developed techniques of higher order abstract syntax and functorial operational semantics to give a compositional and fully abstract semantics for the π-calculus equipped with open bisimulation. The key novelty in our work is the realisation that the sophistication of open bisimulation requires us to move from the usual semantic domain of presheaves over subcategories of Set to presheaves over subcategories of Rel. This extra structure is crucial in controlling the renaming of extruded names and in providing a variety of different dynamic allocation operators to model the different binders of the π-calculus.
Relationally staged computation in the p-calculus
We propose a coalgebraic model of the Fusion calculus based on HD-automata. The main advantage of... more We propose a coalgebraic model of the Fusion calculus based on HD-automata. The main advantage of the approach is that the partition refinement algorithm designed for HD-automata is easily adapted to handle Fusion calculus processes. Hence, the transition systems of Fusion calculus processes can be minimised according to the notion of observational semantics of the calculus. As a beneficial side effect, this also provides a bisimulation checker for Fusion calculus.
We investigate a category theoretic model where both "variables" and "names", usually viewed as s... more We investigate a category theoretic model where both "variables" and "names", usually viewed as separate notions, are particular cases of the more general notion of distinction. The key aspect of this model is to consider functors over the category of irreflexive, symmetric finite relations. The models previously proposed for the notions of "variables" and "names" embed faithfully in the new one, and initial algebra/final coalgebra constructions can be transferred from the formers to the latter. Moreover, the new model allows for defining distinction-aware simultaneous substitutions as clone-like structures. Finally, we apply this model to develop the first semantic interpretation of the FOλ ∇ logic.
HD-automata are a syntax-independent operational model introduced for dealing with history-depend... more HD-automata are a syntax-independent operational model introduced for dealing with history-dependent formalisms. This kind of enriched automata, where states, transitions, and labels are equipped with names and symmetries, have been successfully applied for modelling early and late bisimulation in π-calculus and hyperbisimulation in Fusion calculus. However, current HD-automata are not adequate for modelling open bisimulation, because in HD-automata two names cannot be unified, while open bisimulation is closed under all possible name substitution respecting name distinctions. In this paper we tackle the problem by integrating in the definition of named sets, the basic building blocks of HD-automata, a notion of distinction: names can coalesce if the distinction allows to. Then, we use HD-automata over named sets with distinctions for modelling the open bisimulation of π-calculus. Finally, we discuss the relationship between named sets with distinctions and their HD-automata, with the categorical counterparts based on presheaf categories.
We extend History Dependent Automata to handle polyadic labels, and using a new symbolic semantic... more We extend History Dependent Automata to handle polyadic labels, and using a new symbolic semantics of fusion calculus we give a mapping into these Polyadic HDA with Negative Transitions, and show that the mapping is adequate with respect to hyperequivalence in the fusion calculus. This lays the grounds for HD-automata-based tools applicable not only to the monadic π-calculus but also to the fusion calculus and polyadic π-calculus, allowing implementation efforts to be focused at a foundational level rather than being multiplied in several tools.
Electronic Notes in Theoretical Computer Science, 2009
We consider a typed lambda-calculus with no function types, only alternating sum and product type... more We consider a typed lambda-calculus with no function types, only alternating sum and product types, so that closed terms represent strategies. We add nondeterminism and consider strategies up to lower (i.e. divergence-insensitive) bisimilarity. We investigate the question: when is a function on strategies definable by an open term (with sufficiently large nondeterminism)? The answer is: when it is "exploratory". This is a kind of iterated continuity property, coinductively defined, that is decidable in the case of a function between finite types. In particular, any exploratory function between countably nondeterministic strategies is definable by a continuum nondeterministic term.
Electronic Notes in Theoretical Computer Science, 2004
We apply the recently developed techniques of higher order abstract syntax and functorial operati... more We apply the recently developed techniques of higher order abstract syntax and functorial operational semantics to give a compositional and fully abstract semantics for the π-calculus equipped with open bisimulation. The key novelty in our work is the realisation that the sophistication of open bisimulation requires us to move from the usual semantic domain of presheaves over subcategories of Set to presheaves over subcategories of Rel. This extra structure is crucial in controlling the renaming of extruded names and in providing a variety of different dynamic allocation operators to model the different binders of the π-calculus.
Relationally staged computation in the p-calculus
We propose a coalgebraic model of the Fusion calculus based on HD-automata. The main advantage of... more We propose a coalgebraic model of the Fusion calculus based on HD-automata. The main advantage of the approach is that the partition refinement algorithm designed for HD-automata is easily adapted to handle Fusion calculus processes. Hence, the transition systems of Fusion calculus processes can be minimised according to the notion of observational semantics of the calculus. As a beneficial side effect, this also provides a bisimulation checker for Fusion calculus.
We investigate a category theoretic model where both "variables" and "names", usually viewed as s... more We investigate a category theoretic model where both "variables" and "names", usually viewed as separate notions, are particular cases of the more general notion of distinction. The key aspect of this model is to consider functors over the category of irreflexive, symmetric finite relations. The models previously proposed for the notions of "variables" and "names" embed faithfully in the new one, and initial algebra/final coalgebra constructions can be transferred from the formers to the latter. Moreover, the new model allows for defining distinction-aware simultaneous substitutions as clone-like structures. Finally, we apply this model to develop the first semantic interpretation of the FOλ ∇ logic.
HD-automata are a syntax-independent operational model introduced for dealing with history-depend... more HD-automata are a syntax-independent operational model introduced for dealing with history-dependent formalisms. This kind of enriched automata, where states, transitions, and labels are equipped with names and symmetries, have been successfully applied for modelling early and late bisimulation in π-calculus and hyperbisimulation in Fusion calculus. However, current HD-automata are not adequate for modelling open bisimulation, because in HD-automata two names cannot be unified, while open bisimulation is closed under all possible name substitution respecting name distinctions. In this paper we tackle the problem by integrating in the definition of named sets, the basic building blocks of HD-automata, a notion of distinction: names can coalesce if the distinction allows to. Then, we use HD-automata over named sets with distinctions for modelling the open bisimulation of π-calculus. Finally, we discuss the relationship between named sets with distinctions and their HD-automata, with the categorical counterparts based on presheaf categories.
We extend History Dependent Automata to handle polyadic labels, and using a new symbolic semantic... more We extend History Dependent Automata to handle polyadic labels, and using a new symbolic semantics of fusion calculus we give a mapping into these Polyadic HDA with Negative Transitions, and show that the mapping is adequate with respect to hyperequivalence in the fusion calculus. This lays the grounds for HD-automata-based tools applicable not only to the monadic π-calculus but also to the fusion calculus and polyadic π-calculus, allowing implementation efforts to be focused at a foundational level rather than being multiplied in several tools.