1. N.K. Bary, A Treatise on Trigonometric Series, I and II (MacMillan, New York, 1964)
2. S.V. Bochkarev, A Method of Averaging in the Theory of Orthogonal Series and Some Problems in the Theory of Bases. Trudy Inst. Steklova, vol. 146 (1978) (Russian). English transl. in Proc. Steklov Inst. Math. 3, 1980
3. L. Grafakos, Modern Fourier Analysis, 2nd ed. (Springer, Berlin, 2009)
4. N.B. Haaser, J.A. Sullivan, Real Analysis. Revised reprint of the 1971 original (Dover Publications, New York, 1991)
5. G.H. Hardy, Divergent Series (Clarendon Press, Oxford, 1949)