V. E. Kapustyan, “The asymptotics of constrained control in optimal singular parabolic problems”, Ukr. Mat. Zhurn., vol. 45, no. 10, pp. 1345–1355, Oct. 1993, Accessed: Apr. 16, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/5939