1. Two-way automata and length-preserving homomorphisms;Birget,1990
2. State-complexity of finite-state devices, state compressibility and incompressibility;Birget,1990
3. Automata on a 2-dimensional tape;Blum,1965
4. Boolean formula-Value problem is in ALOGTIME;Buss,1987
5. Alternation;Chandra;J. ACM,1981