∀ {M₀ : Type u_7} {N₀ : Type u_8} [inst : MulZeroOneClass M₀] [inst_1 : MulZeroOneClass N₀]
  [inst_2 : DecidablePred fun x => x = 0] [inst_3 : Nontrivial M₀] [inst_4 : NoZeroDivisors M₀] [Nontrivial N₀]
  {x : M₀}, 1 x = 1 ↔ x ≠ 0