Naidenova, Milka, Nedelcho Milev, and G. Kostadinov. “A Classification of the Uniform Coverings”. Ann. Sofia Univ. Fac. Math. and Inf. 99 (December 12, 2009): 121–127. Accessed November 22, 2024. https://annual.uni-sofia.bg/index.php/fmi/article/view/116.