Categories with Families: Unityped, Simply Typed, and Dependently Typed

Pierre Clairambault (1, 2, 3) , Simon Castellan (4) , Peter Dybjer (5)

1 LIP - Laboratoire de l'Informatique du Parallélisme
2 PLUME - Preuves et Langages
3 CNRS - Centre National de la Recherche Scientifique
4 CELTIQUE - Software certification with semantic analysis
5 Chalmers University of Technology [Gothenburg, Sweden]

We show how the categorical logic of untyped, simply typed and dependently typed lambda calculus can be structured around the notion of category with family (cwf). To this end we introduce subcategories of simply typed cwfs (scwfs), where types do not depend on variables, and unityped cwfs (ucwfs), where there is only one type. We prove several equivalence and biequivalence theorems between cwf-based notions and basic notions of categorical logic, such as cartesian operads, Lawvere theories, categories with finite products and limits, cartesian closed categories, and locally cartesian closed categories. Some of these theorems depend on the restrictions of contextuality (in the sense of Cartmell) or democracy (used by Clairambault and Dybjer for their biequivalence theorems). Some theorems are equivalences between notions with strict preservation of chosen structure. Others are biequivalences between notions where properties are only preserved up to isomorphism. In addition to this we discuss various constructions of initial ucwfs, scwfs, and cwfs with extra structure.

Domaines: Logique en informatique [cs.LO]; Langage de programmation [cs.PL]

Pierre Clairambault, Simon Castellan, Peter Dybjer. Categories with Families: Unityped, Simply Typed, and Dependently Typed. Joachim Lambek: The Interplay of Mathematics, Logic, and Linguistics, 20, Springer International Publishing, pp.135-180, 2021, Outstanding Contributions to Logic, ⟨10.1007/978-3-030-66545-6_5⟩. ⟨hal-03419296⟩