GirikE. A. “On the Existence of Vector Fields With a Given Set of Singular Points on a Two-Dimensional Closed Oriented Manifold”. Ukrains’kyi Matematychnyi Zhurnal 45, no. 12 (December 25, 1993): 1706–1709. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5980.