apply False.elim
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
n : ℕ
x✝ : Positive 0
⊢ ∃ m, step m ≃ 0
case h
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
n : ℕ
x✝ : Positive 0
⊢ False