AL-ZAMEL, A., and R. KHALIL. “ALTERNATION THEOREM FOR $C(I,X)$ AND APPLICATION TO BEST LOCAL APPROXIMATION”. Tamkang Journal of Mathematics 24, no. 2 (June 1, 1993): 135–147. Accessed May 7, 2024. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/4483.