∀ {X Y S : Type u_1} {f : X ⟶ S} {g : Y ⟶ S} (c : CategoryTheory.Limits.PullbackCone f g)
  (x : CategoryTheory.Limits.IsLimit c),
  c.fst =
    CategoryTheory.CategoryStruct.comp (Equiv.ofBijective c.toPullbackObj ⋯).toIso.hom
      (CategoryTheory.Limits.PullbackCone.fst (CategoryTheory.Limits.Types.pullbackLimitCone f g).cone)