proposition: Lemma isaprop_Pullbacks: isaprop (Pullbacks C).
proof: Proof. apply impred; intro a; apply impred; intro b; apply impred; intro c; apply impred; intro f; apply impred; intro g; apply invproofirrelevance. intros Pb Pb'. apply subtypePath. - intro; apply isofhleveltotal2. + apply C. + intros; apply isaprop_isPullback. - apply (total2_paths_f (isotoid _ H (z_iso_from_Pullback_to_Pullback Pb Pb' ))). rewrite transportf_dirprod, transportf_isotoid. rewrite inv_from_z_iso_z_iso_from_Pullback. rewrite transportf_isotoid. rewrite inv_from_z_iso_z_iso_from_Pullback. destruct Pb as [Cone bla]; destruct Pb' as [Cone' bla']; simpl in *. destruct Cone as [p [h k]]; destruct Cone' as [p' [h' k']]; simpl in *. unfold from_Pullback_to_Pullback; rewrite PullbackArrow_PullbackPr2, PullbackArrow_PullbackPr1. apply idpath. Qed.
imports: UniMath.Foundations.All UniMath.MoreFoundations.All UniMath.CategoryTheory.Core.Categories UniMath.CategoryTheory.Core.Isos UniMath.CategoryTheory.Core.NaturalTransformations UniMath.CategoryTheory.Core.TransportMorphisms UniMath.CategoryTheory.Core.Univalence UniMath.CategoryTheory.Core.Functors UniMath.CategoryTheory.Limits.Terminal UniMath.CategoryTheory.Limits.BinProducts UniMath.CategoryTheory.Limits.Equalizers UniMath.CategoryTheory.FunctorCategory UniMath.CategoryTheory.Monics