B. I. Ptashnik, “Some Pseudoparabolic Variational Inequalities with Higher Derivatives”, Ukr. Mat. Zhurn., vol. 54, no. 1, pp. 94–105, Jan. 2002, Accessed: Feb. 16, 2026. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/4043