case step =>
  intro n (ih : n + step m ≃ step (n + m))
  show step n + step m ≃ step (step n + m)
  calc
    step n + step m     ≃ _ := Addition.step_add
    step (n + step m)   ≃ _ := AA.subst₁ ih
    step (step (n + m)) ≃ _ := AA.subst₁ (Rel.symm Addition.step_add)
    step (step n + m)   ≃ _ := Rel.refl
ℕ : Type
inst✝² : Core ℕ
inst✝¹ : Induction ℕ
inst✝ : Addition ℕ
n m : ℕ
⊢ ∀ (m_1 : ℕ), m_1 + step m ≃ step (m_1 + m) → step m_1 + step m ≃ step (step m_1 + m)
no goals