Abstract
G. Freud had wide research interests which included Fourier series. In this survey paper we intend to show the great influence of his only paper [2] on strong approximation of Fourier series. This article has been the origin of a new subject called nowadays “converse-type results for strong approximation of Fourier series.” Before stating his initial result we outline briefly the background of the subject. After the classical result of Fejer in 1904 on the convergence of the arithmetical mean of the partial sums of a Fourier series of 2x-periodic functions, Hardy and Littlewood [3] began to investigate the problem of so-called strong summability. It turned out that under certain conditions not only the means
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