Under mild conditions on the weight function K we characterize lacunary series in the so-called QK spaces.

By well known results of probability theory, any sequence of random variables with bounded second moments has a subsequence satisfying the central limit theorem and the law of the iterated logarithm in a randomized form. In this paper we give criteria for a sequence (Xn) of random variables to have a subsequence (Xnk) whose weighted partial sums, suitably normalized, converge weakly to a stable...