Do Long Van Bertrand Le Saëc Igor Litovsky Characterizations of Rational omega-Languages by Means of Right Congruences. 1-21 1995 143 Theor. Comput. Sci. 1 db/journals/tcs/tcs143.html#VanSL95 http://dx.doi.org/10.1016/0304-3975(95)80022-2