Hladysh BI, Prishlyak OO. Functions with nondegenerate critical points on the boundary of the surface. Ukr. Mat. Zhurn. [Internet]. 2016 Jan. 25 [cited 2025 Apr. 16];68(1):28-37. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/1819