Ptashnik, B. I. “Some Pseudoparabolic Variational Inequalities With Higher Derivatives”. Ukrains’kyi Matematychnyi Zhurnal 54, no. 1 (January 25, 2002): 94–105. Accessed December 6, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/4043.