calc
  n + (d + e) ≃ _ := Rel.symm AA.assoc
  (n + d) + e ≃ _ := AA.substL ‹n + d ≃ m›
  m + e       ≃ _ := ‹m + e ≃ 0›
  0           ≃ _ := 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 k : ℕ
x✝¹ : n ≤ m
d : ℕ
h✝¹ : n + d ≃ m
x✝ : m ≤ 0
e : ℕ
h✝ : m + e ≃ 0
⊢ n + (d + e) ≃ 0
no goals