case step =>
  intro n (ih : n * 0 ≃ 0)
  show step n * 0 ≃ 0
  calc
    step n * 0 ≃ _ := step_mul
    n * 0 + 0  ≃ _ := AA.substL ih
    0 + 0      ≃ _ := Addition.zero_add
    0          ≃ _ := Rel.refl
ℕ : Type
inst✝⁵ : Core ℕ
inst✝⁴ : Induction ℕ
inst✝³ : Addition ℕ
inst✝² : Sign ℕ
inst✝¹ : Order ℕ
inst✝ : Multiplication ℕ
n : ℕ
⊢ ∀ (m : ℕ), m * 0 ≃ 0 → step m * 0 ≃ 0
no goals