∀ {M N P : Type u} [inst : AddCommMonoid M] [inst_1 : AddCommMonoid N] [inst_2 : AddCommMonoid P] (f : M →+ N)
  (g : N →+ P),
  AddCommMonCat.ofHom (g.comp f) = CategoryTheory.CategoryStruct.comp (AddCommMonCat.ofHom f) (AddCommMonCat.ofHom g)