have : n₁ + m ≃ n₂ + m := AA.substL ‹n₁ ≃ n₂›
ℕ : Type
inst✝ : Natural ℕ
n₁ n₂ m : ℕ
x✝ : n₁ ≃ n₂
⊢ n₁——m ≃ n₂——m
ℕ : Type
inst✝ : Natural ℕ
n₁ n₂ m : ℕ
x✝ : n₁ ≃ n₂
this : n₁ + m ≃ n₂ + m
⊢ n₁——m ≃ n₂——m