BabenkoV. F., and GlushkoV. N. “On the Uniqueness of Elements of the Best Approximation and the Best One-Sided Approximation in the Space $L_1$”. Ukrains’kyi Matematychnyi Zhurnal 46, no. 5 (May 25, 1994): 475–483. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5711.