. This work investigates inductive theorem proving techniques for first-order functions whose meaning and domains can be specified by Horn Clauses built up from the equality and finitely many unary membership predicates. In contrast with other works in the area, constructors are not assumed to be free. Techniques originating from tree automata are used to describe ground constructor terms in normal form, on which the induction proofs are built up. Validity of (free) constructor clauses is checked by an original technique relying on the recent discovery of a complete axiomatisation of finite trees and their rational subsets. Validity of clauses with defined symbols or non-free constructor terms is reduced to the latter case by appropriate inference rules using a notion of ground reducibility for these symbols. We show how to check this property by generating proof obligations which can be passed over to the inductive prover. 1 Introduction The need for large formal proofs has lead to t...

The focus of this chapter is the incremental presentation of partial firstorder logic, seen as a powerful framework where the specification of most data types can be directly represented in the most natural way. Both model theory and logical deduction are described in full detail. Alternatives to partiality, like (variants of) error algebras and order-sortedness are also discussed, showing their uses and limitations. Moreover, both the total and the partial (positive) conditional fragment are investigated in detail, and in particular the existence of initial (free) models for such restricted logical paradigms is proved. Some more powerful algebraic frameworks are sketched at the end. Equational specifications introduced in last chapter, are a powerful tool to represent the most common data types used in programming languages and their semantics. Indeed, Bergstra and Tucker have shown in a series of papers (see [BT87] for a complete exposition of results) that a data type is semicompu...

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For the specification of abstract data types, quite a number of logical systems have been developed. In this work, we will try to give an overview over this variety. As a prerequisite, we first study notions of {\em representation} and embedding between logical systems, which are formalized as {\em institutions} here. Different kinds of representations will lead to a looser or tighter connection of the institutions, with more or less good possibilities of faithfully embedding the semantics and of re-using proof support. In the second part, we then perform a detailed ``empirical'' study of the relations among various well-known institutions of total, order-sorted and partial algebras and first-order structures (all with Horn style, i.e.\ universally quantified conditional, axioms). We thus obtain a {\em graph} of institutions, with different kinds of edges according to the different kinds of representations between institutions studied in the first part. We also prove some separation results, leading to a {\em hierarchy} of institutions, which in turn naturally leads to five subgraphs of the above graph of institutions. They correspond to five different levels of expressiveness in the hierarchy, which can be characterized by different kinds of conditional generation principles. We introduce a systematic notation for institutions of total, order-sorted and partial algebras and first-order structures. The notation closely follows the combination of features that are present in the respective institution. This raises the question whether these combinations of features can be made mathematically precise in some way. In the third part, we therefore study the combination of institutions with the help of so-called parchments (which are certain algebraic presentations of institutions) and parchment morphisms. The present book is a revised version of the author's thesis, where a number of mathematical problems (pointed out by Andrzej Tarlecki) and a number of misuses of the English language (pointed out by Bernd Krieg-Br\"uckner) have been corrected. Also, the syntax of specifications has been adopted to that of the recently developed Common Algebraic Specification Language {\sc Casl} \cite{CASL/Summary,Mosses97TAPSOFT}.

Linguisticandsemanticconsequences ofcombining theideasoforder sortedalgebras #asinOBJ# andgeneratorinduction#asinLARCH#areinvestigated.Itisfoundthat onecangaintheadvantagesofboth,inadditiontoincreased#exibilityinde#ning signaturesandgeneratorbases.Ourtreatmentalsogives risetotypingcontrolstronger inacertainsense thanthatofOBJ,aswellasthedetectionofinherentlyinconsistent signatures. Keywordsandphrases:Algebraicspeci#cation,order sortedalgebras,generator induction,functionalprogramming. Contents 1Introduction 2 2Order Sorted Algebras 3 3Generator Induction 7 4Order Sorted Generator Induction 13 5Implementation Considerations 18 6Function De#nition 20 7 Conclusion 21 1 1 INTRODUCTION 2 1 Introduction Goguen et al#5,6,7,8#haveintroduced theconceptofordersortedalgebrasasabasic mechanisminthespeci#cationlanguageOBJ. Anorder sortedalgebraisamany-sorted algebrawithapartialorderde#nedonthe set ofsorts,representingthesubsortrelation. Thepurposeistoobtainincreased#exibilitywithinare...

In an algebraic framework, where equational, membership and existence formulas can be expressed, decorated terms and rewriting provide operational semantics and decision procedures for these formulas. We focus in this work on testing sort inheritance, an undecidable property of specifications, needed for unification in this context. A test and three specific processes, based on completion of a set of rewrite rules, are proposed to check sort inheritance. They depend on the kinds of membership formulas (t : A) allowed in the specifications: flat and linear, shallow and general terms t are studied.

It is widely recognized that equational logic is simple, (relatively) decidable, and (relatively) easily mechanized. But it is also widely thought that equational logic has limited applicability because it cannot handle subtypes or partial functions. We show that a modest stretch of equational logic effectively handles these features. Space limits preclude a full theoretical treatment, so we often sketch, motivate and exemplify.

Types (or sorts) are pervasive in computer science and in rewritingbased programming languages, which often support subtypes (subsorts) and subtype polymorphism. Programs in these languages can be modeled as order-sorted term rewriting systems (OS-TRSs). Often, termination of such programs heavily depends on sort information. But few techniques are currently available for proving termination of OS-TRSs; and they often fail for interesting OS-TRSs. In this paper we generalize the dependency pairs approach to prove termination of OS-TRSs. Preliminary experiments suggest that this technique can succeed where existing ones fail, yielding easier and simpler termination proofs.

We translate OBJ3 to CASL. At the level of basic specifications, we set up several institution representations between the underlying institutions. They correspond to different methodological views of OBJ3. The translations can be the basis for automated tools translating OBJ3 to CASL.

Data Types and Algebraic Semantics The history of programming languages, and to a large extent of software engineering as a whole, can be seen as a succession of ever more powerful abstraction mechanisms. The first stored program computers were programmed in binary, which soon gave way to assembly languages that allowed symbolic codes for operations and addresses. fortran began the spread of "high level" programming languages, though at the time it was strongly opposed by many assembly programmers; important features that developed later include blocks, recursive procedures, flexible types, classes, inheritance, modules, and genericity. Without going into the philosophical problems raised by abstraction (which in view of the discussion of realism in Section 4 may be considerable), it seems clear that the mathematics used to describe programming concepts should in general get more abstract as the programming concepts get more abstract. Nevertheless, there has been great resistance to u...