Douglas S. Bridges Hajime Ishihara Peter M. Schuster Luminita Vîta Apartness, compactness and nearness. 3-10 2008 405 Theor. Comput. Sci. 1-2 http://dx.doi.org/10.1016/j.tcs.2008.06.019 db/journals/tcs/tcs405.html#BridgesISV08