Game Semantics for Martin-L\"of Type Theory

TL;DR

This paper introduces a novel game semantics for Martin-Löf type theory, providing a mathematical and intensional interpretation of dependent types and universes, with strategies resembling algorithms for proofs or programs.

Contribution

It proposes a new category of games that interprets MLTT with dependent types and universes, achieving a surjective and injective semantics for the first time.

Findings

Provides a new mathematical framework for MLTT semantics.

Achieves an intuitive yet precise interpretation of dependent types.

Strategies can be viewed as algorithms for proofs or programs.

Abstract

We present a new game semantics for Martin-L\"of type theory (MLTT), our aim is to give a mathematical and intensional explanation of MLTT. Specifically, we propose a category with families of a novel variant of games, which induces a surjective and injective (when Id-types are excluded) interpretation of the intensional variant of MLTT equipped with unit-, empty-, N-, dependent product, dependent sum and Id-types as well as the cumulative hierarchy of universes for the first time in the literature (as far as we are aware), though the surjectivity is accomplished merely by an inductive definition of a certain class of games and strategies. Our games generalize the existing notion of games, and achieve an interpretation of dependent types and the hierarchy of universes in an intuitive yet mathematically precise manner, our strategies can be seen as algorithms underlying programs (or proofs) in MLTT. A more fine-grained interpretation of Id-types is left as future work.