In the "little theories" version of the axiomatic method, different portions of mathematics are developed in various different formal axiomatic theories. Axiomatic theories may be related by inclusion or by theory interpretation. We argue that the little theories approach is a desirable way to formalize mathematics, and we describe how imps, an Interactive Mathematical Proof System, supports it.

Theory interpretation is a logical technique for relating one axiomatic theory to another with important applications in mathematics and computer science as well as in logic itself. This paper presents a method for theory interpretation in a version of simple type theory, called lutins, which admits partial functions and subtypes. The method is patterned on the standard approach to theory interpretation in rstorder logic. Although the method is based on a nonclassical version of simple type theory, it is intended as a guide for theory interpretation in classical simple type theories as well as in predicate logics with partial functions.

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...

1 other equally abstract theories. Theory interpretations provide the mechanism for transporting theorems. The little theories style of the axiomatic method is employed extensively in mathematical practice; in [4], we discuss its benets for mechanical theorem provers, and how the approach is used in imps. Logic. Standard mathematical reasoning in many areas focuses on functions and their properties, together with operations on functions. For this reason, imps is based on a version of simple type theory. 1 However, we have adopted a version, called lutins, 2 containing partial functions, because they are ubiquitous in both mathematics and computer science. Although terms, such as 2=0, may be nondenoting, the logic is bivalent and formulas always have a truth value. In particular, an atomic formula is false if any of its constituents is nondenoting. This conventio

The little theories method, in which mathematical reasoning is distributed across a network of theories, is a powerful technique for describing and analyzing complex systems. This paper presents an infrastructure for intertheory reasoning that can support applications of the little theories method. The infrastructure includes machinery to store theories and theory interpretations, to store known theorems of a theory with the theory, and to make denitions in a theory by extending the theory "in place". The infrastructure is an extension of the intertheory infrastructure employed in the imps Interactive Mathematical Proof System.

. Although set theory is the most popular foundation for mathematics, not many mechanized mathematics systems are based on set theory. Zermelo-Fraenkel (zf) set theory and other traditional set theories are not an adequate foundation for mechanized mathematics. stmm is a version of von-Neumann-Bernays-Godel (nbg) set theory that is intended to be a Set Theory for Mechanized Mathematics. stmm allows terms to denote proper classes and to be undened, has a denite description operator, provides a sort system for classifying terms by value, and includes lambdanotation with term constructors for function application and function abstraction. This paper describes stmm and discusses why it is a good foundation for mechanized mathematics. Keywords: Set theory, nbg, higher-order logic, mechanized mathematics, theorem proving systems, partial functions, undenedness, sorts. 1.

Mathematics is a process of creating, exploring, and connecting mathematical models. This paper presents an overview of a formal framework for managing the mathematics process as well as the mathematical knowledge produced by the process. The central idea of the framework is the notion of a biform theory which is simultaneously an axiomatic theory and an algorithmic theory. Representing a collection of mathematical models, a biform theory provides a formal context for both deduction and computation. The framework includes facilities for deriving theorems via a mixture of deduction and computation, constructing sound deduction and computation rules, and developing networks of biform theories linked by interpretations. The framework is not tied to a specific underlying logic; indeed, it is intended to be used with several background logics simultaneously. Many of the ideas and mechanisms used in the framework are inspired by the imps Interactive Mathematical Proof System and the Axiom computer algebra system.

Every mathematician will agree that the discovery, analysis, and communication

Abstract. Undefined terms are commonplace in mathematics, particularly in calculus. The traditional approach to undefinedness in mathematical practice is to treat undefined terms as legitimate, nondenoting terms that can be components of meaningful statements. The traditional approach enables statements about partial functions and undefined terms to be stated very concisely. Unfortunately, the traditional approach cannot be easily employed in a standard logic in which all functions are total and all terms are defined, but it can be directly formalized in a standard logic if the logic is modified slightly to admit undefined terms and statements about definedness. This paper demonstrates this by defining a version of simple type theory called Simple Type Theory with Undefinedness (sttwu) and then formalizing in sttwu examples of undefinedness arising in calculus. The examples are taken from M. Spivak’s well-known textbook Calculus. 1

Partial functions can be easily represented in set theory as certain sets of ordered pairs. However, classical set theory provides no special machinery for reasoning about partial functions. For instance, there is no direct way of handling the application of a function to an argument outside its domain as in partial logic. There is also no utilization of lambda-notation and sorts or types as in type theory. This paper introduces a version of von-Neumann-Bernays-Gödel set theory for reasoning about sets, proper classes, and partial functions represented as classes of ordered pairs. The underlying logic of the system is a partial first-order logic, so classvalued terms may be nondenoting. Functions can be specified using lambda-notation, and reasoning about the application of functions to arguments is facilitated using sorts similar to those employed in the logic of the imps Interactive Mathematical Proof System. The set theory is intended to serve as a foundation for mechanized mathematics systems.