∀ {C : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} C] {W : CategoryTheory.MorphismProperty C}
  [W.HasLeftCalculusOfFractions] {X Y : C} (φ : W.RightFraction X Y),
  ∃ ψ, CategoryTheory.CategoryStruct.comp φ.f ψ.s = CategoryTheory.CategoryStruct.comp φ.s ψ.f