Lavrenyuk, S. P. “Systems of Parabolic Variational Inequalities Without Initial Conditions”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 4 (April 25, 1997): 540–547. Accessed December 5, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/5029.