have : n₁ ≃ n₂ := AA.inject ‹step n₁ ≃ step n₂›
ℕ : Type
inst✝² : Core ℕ
inst✝¹ : Induction ℕ
inst✝ : Addition ℕ
n₁✝ n₂✝¹ m n₁ : ℕ
ih : ∀ (y : ℕ), n₁ ≃ y → n₁ + m ≃ y + m
n₂✝ n₂ : ℕ
x✝ : step n₁ ≃ step n₂
⊢ step n₁ + m ≃ step n₂ + m
ℕ : Type
inst✝² : Core ℕ
inst✝¹ : Induction ℕ
inst✝ : Addition ℕ
n₁✝ n₂✝¹ m n₁ : ℕ
ih : ∀ (y : ℕ), n₁ ≃ y → n₁ + m ≃ y + m
n₂✝ n₂ : ℕ
x✝ : step n₁ ≃ step n₂
this : n₁ ≃ n₂
⊢ step n₁ + m ≃ step n₂ + m