fact: Definition is_iso' {C : precategory} {b c : C} (f : b --> c) := ∏ a, isweq (postcomp_with f (a:=a)).
imports: UniMath.Foundations.PartA UniMath.Foundations.Propositions UniMath.Foundations.Sets UniMath.MoreFoundations.Tactics UniMath.CategoryTheory.Core.Categories