have : m ≤ n₂ := AA.substRFn ‹n₁ ≃ n₂› ‹m ≤ n₁›
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n₁ n₂ m : ℕ
x✝¹ : n₁ ≃ n₂
x✝ : m < n₁
left✝ : m ≤ n₁
right✝ : m ≄ n₁
⊢ m < n₂
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n₁ n₂ m : ℕ
x✝¹ : n₁ ≃ n₂
x✝ : m < n₁
left✝ : m ≤ n₁
right✝ : m ≄ n₁
this : m ≤ n₂
⊢ m < n₂