match ‹a ≃ 0 ∨ b ≃ 0› with
| Or.inl (_ : a ≃ 0) => calc
  a * b ≃ _ := AA.substL ‹a ≃ 0›
  0 * b ≃ _ := AA.absorbL
  0     ≃ _ := Rel.refl
| Or.inr (_ : b ≃ 0) => calc
  a * b ≃ _ := AA.substR ‹b ≃ 0›
  a * 0 ≃ _ := AA.absorbR
  0     ≃ _ := Rel.refl
ℕ : Type
inst✝⁵ : Natural ℕ
ℤ : Type
inst✝⁴ : Core ℤ
inst✝³ : Addition ℤ
inst✝² : Multiplication ℤ
inst✝¹ : Negation ℤ
inst✝ : Sign ℤ
a b : ℤ
x✝ : a ≃ 0 ∨ b ≃ 0
⊢ a * b ≃ 0
no goals