A characterization of the words occurring as factors in a minimum number of words.

Ioan Tomescu A characterization of the words occurring as factors in a minimum number of words. 329-331 2006 352 Theor. Comput. Sci. 1-3 http://dx.doi.org/10.1016/j.tcs.2005.11.042 db/journals/tcs/tcs352.html#Tomescu06