Bekmaganbetov, K.A., et al. “Order of the Trigonometric Widths of the Nikol’skii-Besov Classes With Mixed Metric in the Metric of Anisotropic Lorentz Spaces”. Bulletin of the Karaganda University. Mathematics Series, vol. 97, no. 1, Mar. 2020, pp. 17-26, doi:10.31489/2020m1/17-26.