Babenko, V. F., and M. E. Tkachenko. “Problem of Uniqueness of an Element of the Best Nonsymmetric L 1-Approximation of Continuous Functions With Values in KB -Spaces”.
Ukrains’kyi Matematychnyi Zhurnal 60, no. 7 (July 25, 2008): 867 – 878. Accessed April 14, 2025.
https://umj.imath.kiev.ua/index.php/umj/article/view/3205.