1. Reversal complexity of counter machines;Chan,1981
2. Nondeterminism Is Essential for Two-way Counter Machines;Chrobak,1984
3. Fooling a two-way automaton or one pushdown store is better than one counter for two-way machines;Ďuriš;Theoret. Comput. Sci.,1982
4. On reversal-bounded counter machines and on pushdown automata with a bound on the size of the pushdown store;Ďuriš,1982
5. Some open problems in the theory of computation as questions about two-way deterministic pushdown automata languages;Gaul;Math. Systems Theory,1977