We present a meta-logic that contains a new quantifier (for encoding "generic judgment") and inference rules for reasoning within fixed points of a given specification. We then specify the operational semantics and bisimulation relations for the finite π-calculus within this meta-logic. Since we

Abstract. Model checking for transition systems specified in π-calculus has been a difficult problem due to the infinite-branching nature of input prefix, name-restriction and scope extrusion. We propose here an approach to model checking for π-calculus by encoding it into a logic which supports reasoning about bindings and fixed points. This logic, called F Oλ ∆ ∇ , is a conservative extension of Church’s Simple Theory of Types with a “generic ” quantifier. By encoding judgments about transitions in pi-calculus into this logic, various conditions on the scoping of names and restrictions on name instantiations are captured naturally by the quantification theory of the logic. Moreover, standard implementation techniques for (higher-order) logic programming are applicable for implementing proof search for this logic, as illustrated in a prototype implementation discussed in this paper. The use of logic variables and eigenvariables in the implementation allows for exploring the state space of processes in a symbolic way. Compositionality of properties of the transitions is a simple consequence of the meta theory of the logic (i.e., cut elimination). We illustrate the benefits of specifying systems in this logic by studying several specifications of modal logics for pi-calculus. These specifications are also executable directly in the prototype implementation of F Oλ ∆ ∇. 1

Abstract. The operational semantics and typing judgements of modern programming and specification languages are often defined using relations and proof systems. In simple settings, logic programming languages can be used to provide rather direct and natural interpreters for such operational semantics. More complex features of specifications such as names and their bindings, proof rules with negative premises, and the exhaustive enumeration of state spaces, all pose significant challenges to conventional logic programming systems. In this paper, we describe a simple architecture for the implementation of deduction systems that allows a specification to interleave between finite success and finite failure. The implementation techniques for this prover are largely common ones from higher-order logic programming, i.e., logic variables, (higherorder pattern) unification, backtracking (using stream-based computation), and abstract syntax based on simply typed λ-terms. We present a particular instance of this prover’s architecture and its prototype implementation, Level 0/1, based on the dual interpretation of (finite) success and finite failure in proof search. We show how Level 0/1 provides a highlevel and declarative implementation of model checking and bisimulation checking for the (finite) π-calculus. 1

. We give a short, direct proof that a logic program is negationcomplete if, and only if, it has the cut-property. The property negationcomplete refers to three-valued models, the cut-property is defined in terms of ESLDNF-computations only. 1

. Knowledge representation based applications require a more complete set of capabilities than those offered by conventional Prolog compilers. Negation is, probably, the most important one. The inclusion of negation among the logical facilities of LP has been a very active area of research, and several techniques have been proposed. However, the negation capabilities accepted by current Prolog compilers are very limited. In this paper, we discuss the possibility to incorporate some of these techniques in a Prolog compiler in an efficient way. Our idea is to mix some of the existing proposals guided by the information provided by a global analysis of the source code. Keywords: Semantics of Negation, Global Analysis, Implementation of Negation. 1 Introduction Knowledge representation based applications are a natural area for logic programming. However, this kind of applications requires a more complete set of capabilities than those offered by conventional Prolog compilers. ...

In this report we give an outline how proof-theoretic notions can be useful for questions related to software maintenance.

We specify the operational semantics and bisimulation relations for the finite π-calculus within a logic that contains the ∇ quantifier for encoding generic judgments and definitions for encoding fixed points. Since we restrict to the finite case, the ability of the logic to unfold fixed points allows this logic to be complete for both the inductive nature of operational semantics and the coinductive nature of bisimulation. The ∇ quantifier helps with the delicate issues surrounding the scope of variables within π-calculus expressions and their executions (proofs). We illustrate several merits of the logical specifications permitted by this logic: they are natural and declarative; they contain no side-conditions concerning names of variables while maintaining a completely formal treatment of such variables; differences between late and open bisimulation relations arise from familar logic distinctions; the interplay between the three quantifiers (∀, ∃, and ∇) and their scopes can explain the differences between early and late bisimulation and between various modal operators based on bound input and output actions; and proof search involving the application of inference rules, unification, and backtracking can provide complete proof systems for one-step transitions, bisimulation, and satisfaction in modal logic. We also illustrate how one can encode