∀ {R : Type u_2} {M : Type u_5} {N : Type u_6} {O : Type u_7} [inst : Semiring R] [inst_1 : Mul M] [inst_2 : Mul N]
  [inst_3 : Mul O] (e₁ : M ≃ N) (e₂ : N ≃ O),
  MonoidAlgebra.mapDomainAddEquiv R (e₁.trans e₂) =
    (MonoidAlgebra.mapDomainAddEquiv R e₁).trans (MonoidAlgebra.mapDomainAddEquiv R e₂)