1. Abramovich, Y.A. and Kitover, A.K.: d-Independence and d-bases, Positivity, 7 (2003), 95–97.
2. Hart, K. P.: The Čech-Stone compactification of the real line, Recent Progress in General Topology, edited by M. Hušek, and J. van Mill, North-Holland, Amsterdam, 1992, pp. 317–352, MR 95g:54004.