⊦ p*(a, b) ↔ (∃ n. rtc(n, a, b))
∃ n. rtc(n, a, b), Pelem(a), ∀ a, b. Pelem(a) ∧ p(a, b) → Pelem(b) ⊦ Pelem(b)
Used terms: b, a