calc
  n₂ + d ≃ _ := Rel.symm (AA.substL ‹n₁ ≃ n₂›)
  n₁ + d ≃ _ := ‹n₁ + 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
n₁ n₂ m : ℕ
x✝¹ : n₁ ≃ n₂
x✝ : n₁ ≤ m
d : ℕ
h✝ : n₁ + d ≃ m
⊢ n₂ + d ≃ m
no goals