Type-theoretic weak factorization systems

Abstract

This article presents three characterizations of the weak factorization systems on finitely complete categories that interpret intensional dependent type theory with Sigma-, Pi-, and Id-types. The first characterization is that the weak factorization system (L,R) has the properties that L is stable under pullback along R and that all maps to a terminal object are in R. We call such weak factorization systems type-theoretic. The second is that the weak factorization system has an Id-presentation: roughly, it is generated by Id-types in the empty context. The third is that the weak factorization system (L, R) is generated by a Moore relation system, a generalization of the notion of Moore paths.