1.
Kasperski A. Approximation of elements of the spaces X^1_ϕ and X_ϕ by nonlinear, singular kernels. Ann. Math. Sil. [Internet]. 1992 Sep. 30 [cited 2025 Apr. 11];6:21-9. Available from: https://journals.us.edu.pl/index.php/AMSIL/article/view/14264