A. O. Prishlyak and A. M. Bondarenko, “Maps of 2-manifolds into the plane”, MFAT, vol. 18, no. 3, pp. 220–229, Sep. 2012, Accessed: Feb. 04, 2026. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/518