=+. Let P be a finitely additive probability measure on a field $0. For Ach, in analogy with (3.1) define

(3.11)

Pº(A) = inf _P(A.), where now the infimum extends over all finite sequences of Fo-sets A, satisfying AC U ,, A ,,. (If countable coverings are allowed, everything is differ-

ent. It can happen that P(?) =0; see Problem 3.3(e).) Let .&º be the class of sets A such that Pº(E) = P(AnE) + PLACE) for all Ecn.