calc
  step n₁ * m  ≃ _ := step_mul
  (n₁ * m) + m ≃ _ := AA.substL ‹n₁ * m ≃ n₂ * m›
  (n₂ * m) + m ≃ _ := Rel.symm step_mul
  step n₂ * m  ≃ _ := 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
n₁✝ n₂✝¹ m n₁ : ℕ
ih : ∀ (y : ℕ), n₁ ≃ y → n₁ * m ≃ y * m
n₂✝ n₂ : ℕ
x✝ : step n₁ ≃ step n₂
this✝ : n₁ ≃ n₂
this : n₁ * m ≃ n₂ * m
⊢ step n₁ * m ≃ step n₂ * m
no goals