Episkoposian, S. A., and T. M. Saghatelyan. “Convergence and Integrability of Series With Monotone Decreasing Coefficients by Chrestenson - Levy Systems”. The Journal of the Indian Mathematical Society, vol. 84, no. 3-4, July 2017, pp. 182-90, doi:10.18311/jims/2017/14850.