Carl Pomerance John Michael Robson Jeffrey Shallit Automaticity II: Descriptional Complexity in the Unary Case. 181-201 1997 180 Theor. Comput. Sci. 1-2 db/journals/tcs/tcs180.html#PomeranceRS97 http://dx.doi.org/10.1016/S0304-3975(96)00189-2