The Deduction Theorem states that a sentence φ logically entails a sentence ψ if and only if the sentence (φ ⇒ ψ) is valid. More generally, a finite set of sentences {φ₁, ... , φ_n} logically entails φ if and only if the compound sentence (φ₁ ∧ ... ∧ φ_n ⇒ φ) is valid.