Stegantseva, P. G., and A. V. Skryabina. “Topologies on the $n$-Element Set That Consistent With Close to the Discrete Topologies on $(n −1)$-Element Set”. Ukrains’kyi Matematychnyi Zhurnal, vol. 73, no. 2, Feb. 2021, pp. 238-4, https://doi.org/10.37863/umzh.v73i2.6174.