The i.-calculus is considered a useful mathematical tool in the study of programming languages, since programs can be identified with I-terms. However, if one goes further and uses bn-conversion to prove equivalence of programs, then a gross simplification is introduced (programs are identified with total functions from calues to values) that may jeopardise the applicability of theoretical results, In this paper we introduce calculi. based on a categorical semantics for computations, that provide a correct basis for proving equivalence of programs for a wide range of notions of computation.

The -calculus is considered an useful mathematical tool in the study of programming languages, since programs can be identified with -terms. However, if one goes further and uses fij-conversion to prove equivalence of programs, then a gross simplification 1 is introduced, that may jeopardise the applicability of theoretical results to real situations. In this paper we introduce a new calculus based on a categorical semantics for computations. This calculus provides a correct basis for proving equivalence of programs, independent from any specific computational model. 1 Introduction This paper is about logics for reasoning about programs, in particular for proving equivalence of programs. Following a consolidated tradition in theoretical computer science we identify programs with the closed -terms, possibly containing extra constants, corresponding to some features of the programming language under consideration. There are three approaches to proving equivalence of programs: ffl T...

This paper studies the interplay between functional application and nondeterministic choice in the context of untyped λ-calculus. We introduce an operational semantics which is based on the idea of must preorder, coming from the theory of process algebras. To characterize this relation, we build a model using the classical inverse limit construction, and we prove it fully abstract using a generalization of Böhm trees.

Plotkin used the models of reduction in order to obtain a semantic characterization of static type inference in the pure -calculus. Here we apply these models to the study of a nondeterministic language, obtaining results analogous to Plotkin's. 1 Introduction The models of reduction are a generalization of the usual syntactic -models for the pure -calculus (see [Plo92] and the references therein). If a term M reduces to a term N then its interpretation in a model of reduction is "smaller than" or equal to the interpretation of N (and not necessarily equal as in -models). Plotkin obtained a series of soundness and completeness results for static type inference with respect to models of reduction. With type inference in mind, it seems natural that M and N be interpreted differently, since it may be possible to infer a type for N but not for M . The study of nondeterministic languages gives rise to an alternative motivation for considering models of reduction. In nondeterministic lang...

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