fact: Definition morphism_class_opp {C : category} (S : morphism_class C) : (morphism_class (op_cat C)) := λ X Y f, (S _ _) (opp_mor f).
imports: UniMath.MoreFoundations.All UniMath.CategoryTheory.Core.Prelude UniMath.CategoryTheory.opp_precat UniMath.ModelCategories.Retract