Flavio D'Alessandro Benedetto Intrigila Stefano Varricchio On the structure of the counting function of sparse context-free languages. 104-117 2006 356 Theor. Comput. Sci. 1-2 http://dx.doi.org/10.1016/j.tcs.2006.01.037 db/journals/tcs/tcs356.html#DAlessandroIV06