P. O. Kasyanov and V. S. Mel'nik, “On properties of subdifferential mappings in Fréchet spaces”, Ukr. Mat. Zhurn., vol. 57, no. 10, pp. 1385–1394, Oct. 2005, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3692