proposition: Lemma Rezk_eta_fully_faithful : fully_faithful Rezk_eta.
proof: Proof. apply (functor_full_img_fully_faithful_if_fun_is _ _ (yoneda A)). apply yoneda_fully_faithful. Defined.
imports: UniMath.Foundations.PartD UniMath.Foundations.Propositions UniMath.Foundations.Sets UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Univalence UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.Categories.HSET.Core UniMath.CategoryTheory.Categories.HSET.Univalence UniMath.CategoryTheory.opp_precat UniMath.CategoryTheory.yoneda UniMath.CategoryTheory.Subcategory.Core UniMath.CategoryTheory.Subcategory.Full UniMath.CategoryTheory.Equivalences.Core UniMath.CategoryTheory.whiskering UniMath.CategoryTheory.precomp_fully_faithful UniMath.CategoryTheory.precomp_ess_surj