Ptashnik, B.I. (2002) “Some Pseudoparabolic Variational Inequalities with Higher Derivatives”, Ukrains’kyi Matematychnyi Zhurnal, 54(1), pp. 94–105. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4043 (Accessed: 6 December 2025).