"In this case, any formula K is intermediate between A and B. More generally, if A and B are two PL formulas, B is a logical consequence of A, and A and B are not logically equivalent, K $\\stackrel{def}{=}$ (x $\\land$ A) $\\lor$ ($\\neg$ x $\\land$ B) is intermediate between A and B for a propositional letter x not occurring in both A and B. Indeed, it is A $\\Rightarrow$ K, K $\\Rightarrow$ B, but K ha" . . . . .