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, vol. 60, no. 7, July 2008, pp. 867 – 878, https://umj.imath.kiev.ua/index.php/umj/article/view/3205.