apply AA.substFn (Rel.symm add_zero)
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
n m : ℕ
x✝ : Positive n
⊢ Positive (n + 0)
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
n m : ℕ
x✝ : Positive n
⊢ Positive n