Joanna Jedrzejowicz Andrzej Szepietowski Shuffle languages are in P. 31-53 2001 250 Theor. Comput. Sci. 1-2 db/journals/tcs/tcs250.html#JedrzejowiczS01 http://dx.doi.org/10.1016/S0304-3975(99)00109-7