S. A. Pichugov, “Smoothness of functions in the metric spaces Lψ”, Ukr. Mat. Zhurn., vol. 64, no. 9, pp. 1214–1232, Sep. 2012, Accessed: Feb. 16, 2026. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/2653