have : m ≃ 1 := calc
  m     ≃ _ := Rel.symm AA.identL
  1 * m ≃ _ := AA.substL (Rel.symm ‹n ≃ 1›)
  n * m ≃ _ := ‹n * m ≃ 1›
  1     ≃ _ := 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 m : ℕ
x✝ : n * m ≃ 1
this✝¹ : Positive (n * m)
left✝ : Positive n
right✝ : Positive m
this✝ : n ≥ 1
this : n > 1 ∨ n ≃ 1
h✝ : n ≃ 1
⊢ n ≃ 1 ∧ m ≃ 1
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 m : ℕ
x✝ : n * m ≃ 1
this✝² : Positive (n * m)
left✝ : Positive n
right✝ : Positive m
this✝¹ : n ≥ 1
this✝ : n > 1 ∨ n ≃ 1
h✝ : n ≃ 1
this : m ≃ 1
⊢ n ≃ 1 ∧ m ≃ 1