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Gandalf is a first-order resolution theorem-prover, optimized for speed and specializing in manipulations of large clauses. In this paper I describe GANDALF TAC, a HOL tactic that proves goals by calling Gandalf and mirroring the resulting proofs in HOL. This call can occur over a network, and a Gandalf server may be set up servicing multiple HOL clients. In addition, the translation of the Gandalf proof into HOL fits in with the LCF model and guarantees logical consistency.

The proofs of the Church-Rosser theorems for fi, j and fi [ j reduction in untyped -calculus are formalized in Isabelle/HOL, an implementation of Higher Order Logic in the generic theorem prover Isabelle.

Abstract. LEO-II is a standalone, resolution-based higher-order theorem prover designed for effective cooperation with specialist provers for natural fragments of higher-order logic. At present LEO-II can cooperate with the first-order automated theorem provers E, SPASS, and Vampire. The improved performance of LEO-II, especially in comparison to its predecessor LEO, is due to several novel features including the exploitation of term sharing and term indexing techniques, support for primitive equality reasoning, and improved heuristics at the calculus level. LEO-II is implemented in Objective Caml and its problem representation language is the new TPTP THF language. 1

. This is description of TPS, a theorem-proving system for classical type theory (Church's typed #-calculus). TPS has been designed to be a general research tool for manipulating wffs of first- and higher-order logic, and searching for proofs of such wffs interactively or automatically, or in a combination of these modes. An important feature of TPS is the ability to translate between expansion proofs and natural deduction proofs. Examples of theorems that TPS can prove completely automatically are given to illustrate certain aspects of TPS's behavior and problems of theorem proving in higher-order logic. AMS Subject Classification: 03-04, 68T15, 03B35, 03B15, 03B10. Key words: higher-order logic, type theory, mating, connection, expansion proof, natural deduction. 1. Introduction TPS is a theorem-proving system for classical type theory ## (Church's typed #-calculus [20]) which has been under development at Carnegie Mellon University for a number years. This paper gives a general...

This paper presents a formalization of finite and infinite sequences in domain theory carried out in the theorem prover Isabelle. The results

this paper we explain how to do so using HOL---an interactive proof assistant for higher-order logic developed by Gordon and others [18]. First, we describe how to build an infrastructure in HOL that supports reasoning about distributed algorithms, including formal theories of predicates, temporal logic, labeled transition systems, simulation of programs, translation of properties, and graphs. Then we demonstrate, via an example, how to use the powerful intuition about events and causality to guide and structure correctness proofs of distributed algorithms. The example used is the verification of PIF (propagation of information with feedback), which is a simple but typical distributed algorithm due to Segall [33]. 1 INTRODUCTION

daws at cs.ru.nl Abstract. We present a language-theoretic approach to symbolic model checking of PCTL over discrete-time Markov chains. The probability with which a path formula is satisfied is represented by a regular expression. A recursive evaluation of the regular expression yields an exact rational value when transition probabilities are rational, and rational functions when some probabilities are left unspecified as parameters of the system. This allows for parametric model checking by evaluating the regular expression for different parameter values, for instance, to study the influence of a lossy channel in the overall reliability of a randomized protocol. 1

A formal verification of the soundness and completeness of Milner's type inference algorithm W for simply typed lambda-terms is presented. Particular attention is paid to the notorious issue of "new" variables. The proofs are carried out in Isabelle/HOL, the HOL instantiation of the generic theorem prover Isabelle.

This paper presents the first machine-checked verification of Milner's type inference algorithm W for computing the most general type of an untyped -term enriched with let-expressions. This term language is the core of most typed functional programming languages and is also known as Mini-ML. We show how to model all the concepts involved, in particular types and type schemes, substitutions, and the thorny issue of "new" variables. Only a few key proofs are discussed in detail. The theories and proofs are developed in Isabelle/HOL, the HOL instantiation of the generic theorem prover Isabelle.