∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] {X Y : C} {f g : X ⟶ Y} (h : f = g)
  (s : CategoryTheory.Limits.Fork f g) (m : s.pt ⟶ (CategoryTheory.Limits.idFork h).pt),
  CategoryTheory.CategoryStruct.comp m (CategoryTheory.Limits.idFork h).ι = s.ι → m = (fun s => s.ι) s