∀ {R : Type u} {M : Type v} [inst : DivisionSemiring R] [inst_1 : AddCommGroup M] [inst_2 : Module Rᵐᵒᵖ M]
  [inst_3 : Module R M] [SMulCommClass R Rᵐᵒᵖ M] (a b : TrivSqZeroExt R M), (a * b)⁻¹ = b⁻¹ * a⁻¹