中文

Directed proof-relevant logical relations in simplicial HoTT

计算机科学中的逻辑 2026-07-09 v1 编程语言

摘要

Intrinsically-typed presentations of type theory often use equality in the meta-language to represent object-language judgmental equality. In such equational syntax, proof-relevant logical relations define computability predicates on judgmental equivalence classes of types and terms. This approach, however, does not directly account for reduction, which is directed and plays a central role in many logical-relations arguments. This paper develops a directed version of proof-relevant logical relations in simplicial homotopy type theory, where reductions are internalized as \emph{inequality types}. We construct object syntax as a directed quotient inductive type. The central observation is that contravariant families in simplicial type theory provide exactly the proof-relevant form of closure under expansion for logical relations: computability evidence can be transported backward along reductions, with the required functoriality and universal property built in. Using this observation, we construct a unary logical relations model with contravariant computability predicates and prove directed Boolean canonicity: every closed Boolean term reduces to either true or false. We then extend the construction to dependent types and universes, where a comonadic flat modality provides the discreteness needed for type conversion and universe predicates. Finally, we adapt the method to binary logical relations, separating vertical reduction from horizontal parametricity and obtaining a proof-relevant account of representation independence.

引用

@article{arxiv.2607.08154,
  title  = {Directed proof-relevant logical relations in simplicial HoTT},
  author = {Runming Li and Harrison Grodin and Robert Harper},
  journal= {arXiv preprint arXiv:2607.08154},
  year   = {2026}
}