 Since the time of George Boole it has been well known that if formula_1 and formula_2, then their logical product formula_3; and if one or both is 0, formula_4.Under this patent, when the logical product of the PICs is 1, the call is billed at a discounted ("family plan") rate; if the product is 0, the undiscounted rate applies.Therefore, if and only if the caller and called person belong to the carrier's family, the discounted rate applies.