apply Signed.positive_defn.mpr
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
n m✝ : ℕ
x✝ : Positive n
m : ℕ
⊢ Positive (step (n + m))
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
n m✝ : ℕ
x✝ : Positive n
m : ℕ
⊢ step (n + m) ≄ 0