  The Expansion Theorem is used (MAL, p. 61) to prove an important result,  that p(x) and q(x) are equivalent in Boole’s algebra if and only if corresponding  modulii are the same, that is, \(p(1)=q(1)\) and \(p(0)=q(0)\). This result  generalizes to functions of several variables. It will not be stated as such in  LT, but will be absorbed in the much more general (if somewhat opaquely  stated) result that will be called the Rule of 0 and 1.