Radzievskaya, E. I., and G. V. Radzievskii. 2005. “On One Extremal Problem for a Seminorm on the Space $l_1$ With Weight”. Ukrains’kyi Matematychnyi Zhurnal 57 (7), 1002–1006. https://umj.imath.kiev.ua/index.php/umj/article/view/3659.