Extensional Rewriting with Sums

Abstract. Inspired by recent work on normalisation by evaluation for sums, we propose a normalising and confluent extensional rewriting theory for the simply-typed λ-calculus extended with sum types. As a corollary of confluence we obtain decidability for the extensional equational theory of simply-typed λ-calculus extended with sum types. Unlike previous decidability results, which rely on advanced rewriting techniques or advanced category theory, we only use standard techniques.

The Attributed Pi Calculus with Priorities

International audienceWe present the attributed $\pi$-calculus for modeling concurrent systems with interaction constraints depending on the values of attributes of processes. The $\pi$-calculus serves as a constraint language underlying the $\pi$-calculus. Interaction constraints subsume priorities, by which to express global aspects of populations. We present a nondeterministic and a stochastic semantics for the attributed $\pi$-calculus. We show how to encode the $\pi$-calculus with priorities and polyadic synchronization $\pi$@ and thus dynamic compartments, as well as the stochastic $\pi$-calculus with concurrent objects spico. We illustrate the usefulness of the attributed $\pi$-calculus for modeling biological systems at two particular examples: Euglena’s spatial movement in phototaxis, and cooperative protein binding in gene regulation of bacteriophage lambda. Furthermore, population-based model is supported beside individual-based modeling. A stochastic simulation algorithm for the attributed $\pi$-calculus is derived from its stochastic semantics. We have implemented a simulator and present experimental results, that confirm the practical relevance of our approach

Higher Order Generalization

Generalization is a fundamental operation of inductive inference. While first order syntactic generalization (anti-unification) is well understood, its various extensions are needed in applications. This paper discusses syntactic higher order generalization in a higher order language 2[1]. Based on the application ordering, we proved the least general generalization exists and is unique up to renaming. An algorithm to compute the least general generalization is presented. Keywords: higher order logic, unification, anti-unification, generalization. 1 Introduction The meaning of the word generalization is so general that we can find its occurrences in almost every area of study. In computer science, especially in the area of artificial intelligence, generalization serves as a foundation of inductive inference, and finds its applications in diverse areas such as inductive logic programming [9], theorem proving [10], program derivation [4][5]. In the strict sense, generalization is a dua..

Automated Generalisation of Function Definitions

We address the problem of finding the common generalisation of a set of Haskell function definitions so that each function can be defined by partial application of the generalisation. By analogy with unification, which derives the most general common specialisation of two terms, we aim to infer the least general common generalisation. This problem has a unique solution in a first-order setting, but not in a higher-order language. We define a smallest minimal common generalisation which is unique and consider how it might be used for automated program improvement. The same function can have many definitions; we risk over-generalisation if equality is not recognised. A normalising rewrite system is used before generalisation, so many equivalent definitions become identical. The generalisation system we describe has been implemented in Haskell.

Declarative and procedural semantics of fuzzy similarity based unification

summary:In this paper we argue that for fuzzy unification we need a procedural and declarative semantics (as opposed to the two valued case, where declarative semantics is hidden in the requirement that unified terms are syntactically – letter by letter – identical). We present an extension of the syntactic model of unification to allow near matches, defined using a similarity relation. We work in Hájek’s fuzzy logic in narrow sense. We base our semantics on a formal model of fuzzy logic programming extended by fuzzy similarities and axioms of predicate calculus with equality. Rules are many valued implications and not Horn clauses. We prove soundness and completeness of fuzzy similarity based unification

A Compact Proof of Decidability for Regular Expression Equivalence

The article describes a compact formalization of the relation between regular expressions and deterministic finite automata, and a formally verified, efficient algorithm for testing regular expression equivalence, both based on the original notion of pointed regular expression

A Structured Set of Higher-Order Problems

Abstract. We present a set of problems that may support the development of calculi and theorem provers for classical higher-order logic. We propose to employ these test problems as quick and easy criteria preceding the formal soundness and completeness analysis of proof systems under development. Our set of problems is structured according to different technical issues and along different notions of semantics (including Henkin semantics) for higher-order logic. Many examples are either theorems or non-theorems depending on the choice of semantics. The examples can thus indicate the deductive strength of a proof system. 1 Motivation: Test Problems for Higher-Order Reasoning Systems Test problems are important for the practical implementation of theorem provers as well as for the preceding theoretical development of calculi, strategies and heuristics. If the test theorems can be proven (resp. the non-theorems cannot) then they ideally provide a strong indication for completeness (resp. soundness). Examples for early publications providing first-order test problems are [21,29,23]. For more than decade now the TPTP library [28] has been developed as a systematically structured electronic repository o