A topological reading of coinductive predicates in dependent type theory

Abstract In the context of dependent type theory, we show that coinductive predicates have an equivalent topological counterpart in terms of coinductively generated positivity relations, introduced by G. Sambin to represent closed subsets in point-free topology. Our work is complementary to a previous one with M. E. Maietti, where we showed that, in dependent type theory, the well-known concept of wellfounded trees has a topological counterpart in terms of proof-relevant inductively generated formal covers used to provide a predicative and constructive representation of complete suplattices. The proofs performed within Martin–Löf’s type theory and the Minimalist Foundation have been checked in the Agda proof assistant.