KasperskiA. (1992) “Approximation of elements of the spaces X^1_ϕ and X_ϕ by nonlinear, singular kernels”, Annales Mathematicae Silesianae, 6, pp. 21-29. Available at: https://journals.us.edu.pl/index.php/AMSIL/article/view/14264 (Accessed: 18May2024).