case step =>
  intro n₂ (_ : 0 ≃ step n₂)
  exact absurd (Rel.symm ‹0 ≃ step n₂›) step_neqv_zero
ℕ : Type
inst✝² : Core ℕ
inst✝¹ : Induction ℕ
inst✝ : Addition ℕ
n₁ n₂✝ m n₂ : ℕ
⊢ ∀ (m_1 : ℕ), 0 ≃ step m_1 → 0 + m ≃ step m_1 + m
no goals