
doi: 10.1007/bf01872107
The author examines Vilenkin analogues of Walsh series results of \textit{P. Simon} for strong convergence [Acta Math. Hung. 49, 425-431 (1987; Zbl 0643.42020)] and for the Sunouchi operator [Acta Math. Hung. 46, 307-310 (1985; Zbl 0591.42019)]. He shows that if \(f\) belongs to the atomic Hardy space \(H^ 1(G_ m)\), for any Vilenkin group \(G_ m\), then \[ \lim_{n\to\infty} \log^{-1} n \sum^ n_{k=0} k^{-1} \| S_ k f\|_ 1= \| f\|_ 1, \] and if \(f\) belongs to the martingale Hardy space \(H(G_ m)\), for a Vilenkin group \(G_ m\) of bounded type, then \[ Tf:= \left(\sum^ \infty_{n=0} | S_{M_ n}f- \sigma_{M_ n} f|^ 2\right)^{{1\over 2}} \] is a bounded operator from \(H(G_ m)\) into \(L^ 1(G_ m)\). He shows this last result never holds if \(G_ m\) is of unbounded type. However, if \(H(G_ m)\) is replaced by \(H^ 1(G_ m)\), then \(T\) can be a bounded operator for some Vilenkin groups of unbounded type. In fact, the author proves that \(T\) is bounded from \(H^ 1(G_ m)\) to \(L^ 2(G_ m)\) if and only if \(m_ k':= M^{-1}_{k+1} \sum^{k-1}_{j= 0} M_{j+1}\log m_ j\) is bounded.
Fourier series in special orthogonal functions (Legendre polynomials, Walsh functions, etc.), strong convergence, atomic Hardy space, dyadic Hardy space, martingale Hardy space, Vilenkin-Fourier series, Sunouchi operator, Vilenkin group, Walsh series
Fourier series in special orthogonal functions (Legendre polynomials, Walsh functions, etc.), strong convergence, atomic Hardy space, dyadic Hardy space, martingale Hardy space, Vilenkin-Fourier series, Sunouchi operator, Vilenkin group, Walsh series
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