∀ {M : Type u_5} {M₂ : Type u_7} {M₃ : Type u_8} [inst : AddCommMonoid M] [inst_1 : AddCommMonoid M₂]
  [inst_2 : AddCommMonoid M₃] (e : M ≃+ M₂) (e₂ : M₂ ≃+ M₃),
  (e.trans e₂).toNatLinearEquiv = e.toNatLinearEquiv ≪≫ₗ e₂.toNatLinearEquiv