 The axioms for propositional quantification are direct counterparts of \((\forall 1)-(\forall 3)\). Call a sentence \(B\) free for a propositional variable \(p\) in \(A\) if, and only if, no free occurrences of \(p\) lies within the scope of a quantification on \(q\), \(\forall q\) or \(\exists q\), where \(q\) is a propositional variable which occurs in \(B\). Now: