∀ {M : Type u_1} [inst : Monoid M] {N : Type u_2} [inst_1 : Monoid N] {φ : M →* N} {A : Type u_4} [inst_2 : AddMonoid A]
  [inst_3 : DistribMulAction M A] {B : Type u_5} [inst_4 : AddMonoid B] [inst_5 : DistribMulAction N B]
  (self : A →ₑ+[φ] B) (x y : A), self.toFun (x + y) = self.toFun x + self.toFun y