Jeff Edmonds Jarek Gryz Dongming Liang Renée J. Miller Mining for empty spaces in large data sets. 435-452 2003 Theor. Comput. Sci. 3 296 http://dx.doi.org/10.1016/S0304-3975(02)00738-7 db/journals/tcs/tcs296.html#EdmondsGLM03