Khadshiivanov, N., & Nikiforov, V. (1993). On the theorems of Borsuk-Ulman and Ljusternik-Shnirelman-Borsuk. Ann. Sofia Univ. Fac. Math. And Inf., 84, 83–89. Retrieved from https://ftl5.uni-sofia.bg/index.php/fmi/article/view/471