Orlov, Igor Vladimirovich, and Svetlana Ivanovna Smirnova. “Invertibility of Multivalued Sublinear Operators”. Eurasian Mathematical Journal 6, no. 4 (December 30, 2015): 44–58. Accessed October 9, 2025. https://emj.enu.kz/index.php/main/article/view/622.