=+P*(ANE) + P*(A'nE) = P*(E)

hold for every set E; (3.3) is the special case E = f2, because it will turn out that P*(22) == 1.1 A set A is called P *- measurable if (3.4) holds for all E; let be the class of such sets. What will be shown is that A contains o(7)

and that the restriction of P* to o(7%) is the required extension of P.