have ⟨d, (_ : step n + d ≃ 0)⟩ := le_defn.mp ‹step n ≤ 0›
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n : ℕ
x✝ : n < 0
this : step n ≤ 0
⊢ False
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n : ℕ
x✝ : n < 0
this : step n ≤ 0
d : ℕ
h✝ : step n + d ≃ 0
⊢ False