∀ {R : Type u_1} {M : Type u_2} [inst : Semiring R] [inst_1 : Add M] (a : (M →₀ R)ᵐᵒᵖ),
  AddMonoidAlgebra.opRingEquiv a =
    Finsupp.equivMapDomain AddOpposite.opEquiv (Finsupp.mapRange MulOpposite.op ⋯ (MulOpposite.unop a))