case step =>
  intro n (ih : n + 0 ≃ n)
  show step n + 0 ≃ step n
  calc
    step n + 0   ≃ _ := Addition.step_add
    step (n + 0) ≃ _ := AA.subst₁ ih
    step n       ≃ _ := Rel.refl
ℕ : Type
inst✝² : Core ℕ
inst✝¹ : Induction ℕ
inst✝ : Addition ℕ
n : ℕ
⊢ ∀ (m : ℕ), m + 0 ≃ m → step m + 0 ≃ step m
no goals