Fine and Wilf's Theorem for Three Periods and a Generalization of Sturmian Words.

Maria Gabriella Castelli Filippo Mignosi Antonio Restivo Fine and Wilf's Theorem for Three Periods and a Generalization of Sturmian Words. 83-94 1999 218 Theor. Comput. Sci. 1 db/journals/tcs/tcs218.html#CastelliMR99 http://dx.doi.org/10.1016/S0304-3975(98)00251-5