fact: Definition Under_mor_mor {X Y : Under_ob} (M : Under_mor X Y) : C⟦Under_ob_cod X, Under_ob_cod Y⟧ := pr1 M.
imports: UniMath.Foundations.PartD UniMath.Foundations.Propositions UniMath.Foundations.Sets UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Functors