Khadshiivanov, Nikolay, and Simeon Stefanov. “On the Identification of Points by Continuous Maps from the Torus to the Plane”. Ann. Sofia Univ. Fac. Math. and Inf. 84 (December 12, 1993): 91–96. Accessed November 25, 2024. https://annual.uni-sofia.bg/index.php/fmi/article/view/472.