1. G. H. Hardy, Divergent Series, The Clarendon Press, Oxford (1963).
2. R. Kuk, Infinite Matrices and Sequence Spaces [in Russian], Fizmatgiz, Moscow (1960).
3. A. I. Markushevich, Elements of the Theory of Analytic Functions [in Russian], Uchpedgiz, Moscow (1944).
4. G. H. Hardy, A Course of Pure Mathematics [Russian translation], IL, Moscow (1949).
5. A. Wilansky, ?A necessary and sufficient condition that a summability method be stronger than convergence,? Bull. Am. Math. Soc.,55, 914?916 (1949).