calc
  n     ≃ _ := Rel.symm add_zero
  n + 0 ≃ _ := ‹n + 0 ≃ m›
  m     ≃ _ := Rel.refl
case h
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
d : ℕ
x✝ : n + 0 ≃ m
⊢ n ≃ m
no goals