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