Fooling a two Way Automaton or one Pushdown Store is better than one Counter for two Way Machines.

Pavol Duris Zvi Galil Fooling a two Way Automaton or one Pushdown Store is better than one Counter for two Way Machines. 39-53 1982 21 Theor. Comput. Sci. db/journals/tcs/tcs21.html#DurisG82 http://dx.doi.org/10.1016/0304-3975(82)90087-1