∀ {C : Type u_3} {D : Type u_5} [inst : CategoryTheory.Category.{u_1, u_3} C]
  [inst_1 : CategoryTheory.Category.{u_6, u_5} D] (L : CategoryTheory.Functor C D) {H : Type u_4}
  [inst_2 : CategoryTheory.Category.{u_2, u_4} H] [inst_3 : ∀ (F : CategoryTheory.Functor C H), L.HasLeftKanExtension F]
  {X Y Z : CategoryTheory.Functor C H} (f : X ⟶ Y) (g : Y ⟶ Z),
  (L.leftKanExtension X).descOfIsLeftKanExtension (L.leftKanExtensionUnit X) (L.leftKanExtension Z)
      (CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp f g) (L.leftKanExtensionUnit Z)) =
    CategoryTheory.CategoryStruct.comp
      ((L.leftKanExtension X).descOfIsLeftKanExtension (L.leftKanExtensionUnit X) (L.leftKanExtension Y)
        (CategoryTheory.CategoryStruct.comp f (L.leftKanExtensionUnit Y)))
      ((L.leftKanExtension Y).descOfIsLeftKanExtension (L.leftKanExtensionUnit Y) (L.leftKanExtension Z)
        (CategoryTheory.CategoryStruct.comp g (L.leftKanExtensionUnit Z)))