1. Bary, N. K.: A treatise on trigonometric series. Pergamon Press, Oxford–London–New York–Paris–Frankfurt, 1964. Zbl 0129.28002
2. Fomin, G. A.: On linear methods for summing Fourier series. Math. Sbornik 66 (1964), 144–152. MR 0168988
3. Garret, W. J., Stanojević, Č. V.: On integrability and $L^1$–convergence of certain cosine sums. Notices, Amer. Math. Soc. 22 (1975), A–166.
4. Garret, W. J., Stanojević, Č. V.: On $L^1$–convergence of certain cosine sums. Proc. Amer. Math. Soc. 54 (1976), 101–105. MR 0394002
5. Hooda, N., Ram, B., Bhatia, S. S.: On $L^1$–convergence of a modified cosine sum. Soochow J. of Math. 28 (3) (2002), 305–310. MR 1926327