1. A. Aho, J. Ullman,The Theory of Parsing, Translation and Compiling, Vol. 1, Prentice-Hall, Englewood Cliffs, NJ, 1972.
2. J. C. Birget, Concatenation of inputs in a two-way automaton,Theoret. Comput. Sci.,63 (1989), 141?156.
3. J. C. Birget, Positional simulation of two-way automata: proof of a conjecture of R. Kannan, and generalizations,J. Comput. System Sci. (special issue onSTOC 89),45 (1992), 154?179.
4. J. C. Birget, Two-way automata and length-preserving homomorphisms, Report # 109, Dept. of Computer Science, University of Nebraska (1990) (submitted).
5. J. C. Birget, The minimum automaton of certain languages (in preparation).