We present C-CoRN, the Constructive Coq Repository at Nijmegen. It consists of a library of constructive algebra and analysis, formalized in the theorem prover Coq. In this paper we explain the structure, the contents and the use of the library. Moreover we discuss the motivation and the (possible) applications of such a library.

Abstract. We describe a framework for algebraic expressions for the proof assistant Coq. This framework has been developed as part of the FTA project in Nijmegen, in which a complete proof of the fundamental theorem of algebra has been formalized in Coq. The algebraic framework that is described here is both abstract and structured. We apply a combination of record types, coercive subtyping and implicit arguments. The algebraic framework contains a full development of the real and complex numbers and of the rings of polynomials over these fields. The framework is constructive. It does not use anything apart from the Coq logic. The framework has been successfully used to formalize non-trivial mathematics as part of the FTA project.

We describe a framework of algebraic structures in the proof assistant Coq. We have developed this framework as part of the FTA project in Nijmegen, in which a constructive proof of the Fundamental Theorem of Algebra has been formalized in Coq. The algebraic hierarchy that is described here is both abstract and way, dening e.g. a ring as a tuple consisting of a group, a binary operation and a constant that together satisfy the properties of a ring. In this way, a ring automatically inherits the group properties of the additive subgroup. The algebraic hierarchy is formalized in Coq by applying a combination of labeled record types and coercions. In the labeled record types of Coq, one can use dependent types: the type of one label may depend on another label. This allows to give a type to a dependent-typed tuple like hA; f; ai, where A is a set, f an operation on A and a an element of A. Coercions are

We have finished a constructive formalization in the theorem prover Coq of the Fundamental Theorem of Calculus, which states that differentiation and integration are inverse processes. In this formalization, we have closely followed Bishop's work ([4]). In this paper, we describe the formalization in some detail, focusing on how some of Bishop's original proofs had to be refined, adapted or redone from scratch.

Abstract. We estimate the cost of formalizing a proper standard library for proof checking of mathematics in the spirit of the QED project. Apparently it will take approximately 140 man-years. This estimate does not include the development of the proof checking program, nor does it include work on the metatheory of that program. This should discourage any individual or small research group to think they can reach anything like the goal of the QED project on their own.

In type-theory based proof systems that provide inductive structures, computation tools are automatically associated to inductive de nitions. Choosing a particular representation for a given concept has a strong inuence on proof structure. We propose a method to make the change from one representation to another easier, by systematically translating proofs from one context to another. We show how this method works by using it on natural numbers, for which a unary representation (based on Peano axioms) and a binary representation are available. This method leads to an automatic translation tool that we have implemented in Coq and successfully applied to several arithmetical theorems.

Abstract. The technique of reflection is a way to automate proof construction in type theoretical proof assistants. Reflection is based on the definition of a type of syntactic expressions that gets interpreted in the domain of discourse. By allowing the interpretation function to be partial or even a relation one gets a more general method known as ``partial reflection''. In this paper we show how one can take advantage of the partiality of the interpretation to uniformly define a family of tactics for equational reasoning that will work in different algebraic structures. The tactics then follow the hierarchy of those algebraic structures in a natural way.

The correctness of proofs is increasingly being veried with computer programs called `proof checkers'. Examples of such proof checkers are Mizar, ACL2, PVS, Nuprl, HOL, Isabelle and Coq. This paper addresses what is one of the most important problems for that kind of system, which is how to deal with partial functions and the related issue of how to treat undened terms. In many systems the problem is avoided by articially making all functions total. However that does not correspond to the practice of every day mathematics. In type theory partial functions are modeled by giving functions extra arguments which are proof objects. Because of that it is not possible to apply a function outside its domain. However having proofs as rst class objects makes the logic non-standard. This has the disadvantages that it is unfamiliar to most mathematicians and that many proof tools won't be usable for it. For instance a theorem prover like Otter cannot be easily used for this kind of logic. Also expressions in type theoretical systems get clumsy because they contain proof objects. The PVS system solves the problem of partial functions dierently. PVS generates type-correctness conditions or TCCs for statements in its language. These are proof obligations that have to be satised `on the side' to show that the statements are well-formed. In this paper we relate the type theoretical approach to one resembling the PVS approach. We add domain conditions to ordinary rst order logic (which in this paper will be classical and one-sorted) and we show that the combination corresponds precisely to a rst order system that treats partial functions in the style of type theory. 1

We have finished a constructive formalization in the theorem prover Coq of the Fundamental Theorem of Calculus, which states that differentiation and integration are inverse processes. This formalization is built upon the library of constructive algebra created in the FTA (Fundamental Theorem of Algebra) project, which is extended with results about the real numbers, namely about (power) series. Two important issues that arose in this formalization and which will be discussed in this paper are partial functions (different ways of dealing with this concept and the advantages of each different approach) and the high level tactics that were developed in parallel with the formalization (which automate several routine procedures involving results about real-valued functions).