Hladysh, B. I., and O. O. Prishlyak. 2019. “Deformations in the General Position of the Optimal functions on Oriented Surfaces With Boundary”. Ukrains’kyi Matematychnyi Zhurnal 71 (8), 1028-39. http://umj.imath.kiev.ua/index.php/umj/article/view/1495.