{α : Type u_5} →
  [inst : Norm α] →
    [inst_1 : Mul α] →
      {motive : NormMulClass α → Sort u} →
        ((norm_mul : ∀ (a b : α), ‖a * b‖ = ‖a‖ * ‖b‖) → motive ⋯) → (t : NormMulClass α) → motive t