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**11 - 16**of**16**### Testing and Proving in Dependent Type Theory (Chapter 1: Introduction)

- CHALMERS UNIVERSITY OF TECHNOLOGY AND GOTEBORG UNIVERSITY
, 2003

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### Under consideration for publication in Math. Struct. in Comp. Science Formalizing Overlap Algebras in Matita

, 2010

"... We describe some formal topological results, formalized in Matita 1/2, presented in predicative intuitionistic logic and in terms of Overlap Algebras. Overlap Algebras are new algebraic structures designed to ease reasoning about subsets in an algebraic way within intuitionistic logic. We find that ..."

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We describe some formal topological results, formalized in Matita 1/2, presented in predicative intuitionistic logic and in terms of Overlap Algebras. Overlap Algebras are new algebraic structures designed to ease reasoning about subsets in an algebraic way within intuitionistic logic. We find that they also ease the formalization of formal topological results in an interactive theorem prover. Our main result is the existence of a functor between two categories of ‘generalized topological spaces’, one with points (Basic Pairs) and the other point-free (Basic Topologies). The reported formalization is part as a wider scientific collaboration with the inventor of the theory, Giovanni Sambin. His goal is to verify in what sense, and with what difficulties, his theory is ‘implementable’. We check that all intermediate constructions respect the stringent size requirements imposed by predicative logic. The formalization is quite unusual, since it has to make explicit size information that is often hidden. We found that the version of Matita used for the formalization was largely inappropriate. The formalization drove several major improvements of Matita that will be integrated in the next major release (Matita 1.0). We show some motivating examples for these improvements, taken directly from the formalization. We also describe a possibly sub-optimal solution in Matita 1/2, exploitable in other similar systems. We briefly discuss a better solution available in Matita 1.0. 1.

### The Interpretation of Inuitionistic . . .

, 2008

"... We give an intuitionistic view of Seely’s interpretation of Martin-Löf’s intuitionistic type theory in locally cartesian closed categories. The idea is to use Martin-Löf type theory itself as metalanguage, and E-categories, the appropriate notion of categories when working in this metalanguage. As a ..."

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We give an intuitionistic view of Seely’s interpretation of Martin-Löf’s intuitionistic type theory in locally cartesian closed categories. The idea is to use Martin-Löf type theory itself as metalanguage, and E-categories, the appropriate notion of categories when working in this metalanguage. As an E-categorical substitute for the formal system of Martin-Löf type theory we use E-categories with families (E-cwfs). These come in two flavours: groupoid-style E-cwfs and proofirrelevant E-cwfs. We then analyze Seely’s interpretation as consisting of three parts. The first part is purely categorical: the interpretation of groupoid-style E-cwfs in E-locally cartesian closed categories. (The key part of this interpretation has been type-checked in the Coq system.) The second is a coherence problem which relates groupoid-style E-cwfs with proofirrelevant ones. The third is a purely syntactic problem: that proof-irrelevant E-cwfs are equivalent to traditional lambda calculus based formulations of Martin-Löf type theory.

### MFPS 29 Preliminary Proceedings Normalization by evaluation and algebraic effects

"... We examine the interplay between computational effects and higher types. We do this by presenting a normalization by evaluation algorithm for a language with function types as well as computational effects. We use algebraic theories to treat the computational effects in the normalization algorithm i ..."

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We examine the interplay between computational effects and higher types. We do this by presenting a normalization by evaluation algorithm for a language with function types as well as computational effects. We use algebraic theories to treat the computational effects in the normalization algorithm in a modular way. Our algorithm is presented in terms of an interpretation in a category of presheaves equipped with partial equivalence relations. The normalization algorithm and its correctness proofs are formalized in dependent type theory (Agda). Keywords: