proposition: Lemma is_functor_functor_opp {C D : precategory} (F : functor C D) : is_functor (functor_opp_data F).
proof: Proof. split; intros. - unfold functor_idax; simpl. apply (functor_id F). - unfold functor_compax; simpl. intros. apply (functor_comp F). Qed.
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