Antoni Koscielski Leszek Pacholski Makanin's Algorithm is not Primitive Recursive. 145-156 1998 191 Theor. Comput. Sci. 1-2 db/journals/tcs/tcs191.html#KoscielskiP98 http://dx.doi.org/10.1016/S0304-3975(96)00321-0