Semenov, Pavel V., and Evgeny V. Shchepin. “Selection Approach to Multivalued Separation Theorems”. Topological Methods in Nonlinear Analysis 14, no. 1 (September 1, 1999): 183–192. Accessed July 6, 2025. https://apcz.umk.pl/TMNA/article/view/TMNA.1999.028.