fact: Definition op_nt {c d : category} {f g : functor c d} (a : nat_trans f g) : nat_trans (functor_opp g) (functor_opp f).
imports: UniMath.Foundations.PartD UniMath.Foundations.Propositions UniMath.MoreFoundations.All UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Isos UniMath.CategoryTheory.Core.NaturalTransformations UniMath.CategoryTheory.Core.Univalence UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.FunctorCategory