∀ {C : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} C] {W : CategoryTheory.MorphismProperty C}
  [inst_1 : W.HasLeftCalculusOfFractions] {X Y Z : C} (z₁ : W.LeftFraction X Y) (z₂ : W.LeftFraction Y Z),
  (CategoryTheory.MorphismProperty.LeftFraction.Localization.Hom.mk z₁).comp
      (CategoryTheory.MorphismProperty.LeftFraction.Localization.Hom.mk z₂) =
    z₁.comp z₂