exact this
case mp.left
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n m : ℕ
x✝ : n < m
this✝¹ : step n ≤ m
k : ℕ
h✝ : step n + k ≃ m
this✝ : step k ≄ 0
this : Positive (step k)
⊢ Positive (step k)
no goals