1. Two-way finite state generators;Culik,1983
2. Computers and Intractability: A Guide to the Theory of NP-Completeness;Garey,1978
3. Regular chain code picture languages of nonlinear descriptional complexity;Hinz,1986
4. Classes of picture languages that cannot be distinguished in the chain code concept and deletion of redundant retreats;Hinz,1989
5. Introduction to Automata Theory, Languages, and Computation;Hopcroft,1979