have ⟨d₁, (_ : n + d₁ ≃ m)⟩ := le_defn.mp ‹n ≤ m›
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n m : ℕ
x✝¹ : n ≤ m
x✝ : m ≤ n
⊢ n ≃ m
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n m : ℕ
x✝¹ : n ≤ m
x✝ : m ≤ n
d₁ : ℕ
h✝ : n + d₁ ≃ m
⊢ n ≃ m