On the Use of Computational Paths in Path Spaces of Homotopy Type Theory

TL;DR

This paper introduces a new approach using computational paths to analyze path spaces in homotopy type theory, offering a simpler alternative to the traditional code-encode-decode method, and demonstrates its effectiveness through key examples.

Contribution

It proposes an alternative, simpler method based on computational paths for defining and working with path spaces in homotopy type theory.

Findings

Constructed the path space of natural numbers.

Calculated the fundamental group of the circle.

Demonstrated the approach's simplicity and effectiveness.

Abstract

The treatment of equality as a type in type theory gives rise to an interesting type-theoretic structure known as `identity type'. The idea is that, given terms $a,b$ of a type $A$, one may form the type $Id_{A}(a,b)$, whose elements are proofs that $a$ and $b$ are equal elements of type $A$. A term of this type, $p : Id_{A}(a,b)$, makes up for the grounds (or proof) that establishes that $a$ is indeed equal to $b$. Based on that, a proof of equality can be seen as a sequence of substitutions and rewrites, also known as a `computational path'. One interesting fact is that it is possible to rewrite computational paths using a set of reduction rules arising from an analysis of redundancies in paths. These rules were mapped by De Oliveira in 1994 in a term rewrite system known as $LND_{EQ}-TRS$. Here we use computational paths and this term rewrite system to work with path spaces. In homotopy type theory, the main technique used to define path spaces is the code-encode-decode approach. Our objective is to propose an alternative approach based on the theory of computational paths. We believe this new approach is simpler and more straightforward than the code-encode-decode one. We then use our approach to obtain two important results of homotopy type theory: the construction of the path space of the naturals and the calculation of the fundamental group of the circle.