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 : ℕ
ih : n * 0 ≃ 0
⊢ step n * 0 ≃ 0
no goals