[1]
A. O. Prishlyak and D. P. Lychak, “Morse functions and flows on nonorientable surfaces”, MFAT, vol. 15, no. 3, pp. 251–258, Sep. 2009, Accessed: Mar. 30, 2026. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/422