∀ {M : Type u_1} {N : Type u_2} {P : Type u_3} [inst : AddZeroClass M] [inst_1 : AddZeroClass N] [inst_2 : AddMonoid P]
  (f : M →+ P) (g : N →+ P), (AddMonoid.Coprod.lift f g).comp AddMonoid.Coprod.inr = g