Definition Given a sentence s, we can say that t p (p for premise), a subtree of s, entails some other subtree t h (h for hypothesis) in the context of s, if: s σ (s, t p , t h , α), where α assigns the slots of t h , and is textual entailment.
if s is true, then replacing t p with t h in s should create a new sentence that is also true.