have ⟨d, (_ : (n + m₁) + d ≃ n + m₂)⟩ := le_defn.mp ‹n + m₁ ≤ n + m₂›
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n m₁ m₂ : ℕ
x✝ : n + m₁ ≤ n + m₂
⊢ m₁ ≤ m₂
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n m₁ m₂ : ℕ
x✝ : n + m₁ ≤ n + m₂
d : ℕ
h✝ : n + m₁ + d ≃ n + m₂
⊢ m₁ ≤ m₂