∀ {ι : Type u_1} {M : Type u_2} [inst : DecidableEq ι] [inst_1 : Semiring M] [inst_2 : (m : M) → Decidable (m ≠ 0)],
  Function.RightInverse addMonoidAlgebraEquivDirectSum.invFun addMonoidAlgebraEquivDirectSum.toFun