Entailment of subtype constraints was introduced for constraint simplification in subtype inference systems. Designing an efficient algorithm for subtype entailment turned out to be surprisingly difficult. The situation was clarified by Rehof and Henglein who proved entailment of structural subtype constraints to be coNP-complete for simple types and PSPACE-complete for recursive types. For entailment of non-structural subtype constraints of both simple and recursive types they proved PSPACE-hardness and conjectured PSPACE-completeness but failed in finding a complete algorithm. In this paper, we investigate the source of complications and isolate a natural subproblem of non-structural subtype entailment that we prove PSPACE-complete. We conjecture (but this is left open) that the presented approach can be extended to the general case.

We present a prescriptive type system with parametric polymorphism and subtyping for constraint logic programs. The aim of this type system is to detect programming errors statically. It introduces a type discipline for constraint logic programs and modules, while maintaining the capabilities of performing the usual coercions between constraint domains, and of typing meta-programming predicates, thanks to the exibility of subtyping. The property of subject reduction expresses the consistency of a prescriptive type system w.r.t. the execution model: if a program is \well-typed", then all derivations starting from a \well-typed" goal are again \well-typed". That property is proved w.r.t. the abstract execution model of constraint programming which proceeds by accumulation of constraints only, and w.r.t. an enriched execution model with type constraints for substitutions. We describe our implementation of the system for type checking and type inference. We report our experimental results on type checking ISO-Prolog, the (constraint) libraries of Sicstus Prolog and other Prolog programs.

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Abstract. In addition to behavioral properties, spatial logics can talk about otherkey properties of concurrent systems such as secrecy, freshness, usage of resources, and distribution. We study an expressive spatial logic for systems speci-fied in the synchronous p-calculus with recursion, based on a small set of behavioral and spatial observations. We give coinductive and equational characteriza-tions of the equivalence induced on processes by the logic, and conclude that it strictly lies between structural congruence and strong bisimulation. We then showthat model-checking is decidable for a useful class of processes that includes the finite-control fragment of the p-calculus.

Abstract. In addition to behavioral properties, spatial logics can talk about otherkey properties of concurrent systems such as secrecy, freshness, usage of resources, and distribution. We study an expressive spatial logic for systems speci-fied in the synchronous p-calculus with recursion, based on a small set of behavioral and spatial observations. We give coinductive and equational characteriza-tions of the equivalence induced on processes by the logic, and conclude that it strictly lies between structural congruence and strong bisimulation. We then showthat model-checking is decidable for a useful class of processes that includes the finite-control fragment of the p-calculus.