calc
  n     ≃ _ := Rel.symm add_zero
  n + 0 ≃ _ := AA.substR (Rel.symm ‹d ≃ 0›)
  n + d ≃ _ := ‹n + d ≃ m›
  m     ≃ _ := Rel.refl
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
left✝ : n ≤ m
right✝ : n ≄ m
d : ℕ
h✝ : n + d ≃ m
x✝ : d ≃ 0
⊢ n ≃ m
no goals