Ligun, A. A., and A. A. Shumeiko. “On One Problem of Minimization of Area”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 7 (July 25, 1997): 927–936. Accessed April 11, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/5083.