∀ {C : Type u} {A : Type u_1} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : AddMonoid A]
  (self : CategoryTheory.ShiftMkCore C A) (m₁ m₂ m₃ : A) (X : C) {Z : C}
  (h : (self.F m₃).obj ((self.F m₂).obj ((self.F m₁).obj X)) ⟶ Z),
  CategoryTheory.CategoryStruct.comp ((self.add (m₁ + m₂) m₃).hom.app X)
      (CategoryTheory.CategoryStruct.comp ((self.F m₃).map ((self.add m₁ m₂).hom.app X)) h) =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.eqToHom ⋯)
      (CategoryTheory.CategoryStruct.comp ((self.add m₁ (m₂ + m₃)).hom.app X)
        (CategoryTheory.CategoryStruct.comp ((self.add m₂ m₃).hom.app ((self.F m₁).obj X)) h))