Kovalevsky , A. A. “Convergence of Solutions of Variation Inequalities With Bilateral Obstacles in Perforated Regions”. Ukrains’kyi Matematychnyi Zhurnal 44, no. 2 (February 28, 1992): 191–197. Accessed December 6, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/7832.