
doi: 10.1007/bf01450077
Let (X,\(\beta\),m) be a probability space and let \(T: L_ 2(X)\to L_ 2(X)\) be a contraction. The series \(\sum ^{\infty}_{n=1}c_ nT^ n\) converges in norm if \(\sum ^{\infty}_{n=1}c_ n\exp (2\pi inx)\) converges uniformly. But also there are many examples of \((c_ n)\) for which \(\sum ^{\infty}_{n=1}| c_ n| =\infty\) and yet the series \(\sum ^{\infty}_{n=1}c_ nT^ nf(x)\) converges a.e. x too. Generally, if \(\sum ^{\infty}_{n=1}| c_ n| ^ 2n^{1/2}\log ^ s(n)2\), then for a.e. choice of \(sign(\gamma _ n)\in \{-1,1\}\), if T is any contraction on \(L_ 2(X)\), the series \(S=\sum ^{\infty}_{n=1}\gamma _ nc_ nT^ n\) converges in norm and for all \(f\in L_ 2(X)\), Sf(X) converges a.e. x. By the same technique, one can show that for all \(\sigma >3/4\), and for all \(f\in L_ 2(X)\), the series \(\sum ^{\infty}_{n=1}(\cos (n \log n)/n^{\sigma})T^ nf(x)\) converges a.e. x. By using complex interpolation, similar results can be obtained in \(L_ p(X)\), \(1
510.mathematics, Strong limit theorems, Sums of independent random variables; random walks, contraction, complex interpolation, Article
510.mathematics, Strong limit theorems, Sums of independent random variables; random walks, contraction, complex interpolation, Article
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