1. Time and tape complexity of pushdown automaton languages;Aho;Inform. Control,1968
2. Two-way finite state generators;Culik,1983
3. Computer processing of line-drawing images;Freeman;Computing Survey,1974
4. Computers and Intractability — A Guide to the Theory of NP-Completeness;Garey,1979
5. The Mathematical Theory of Context-Free Languages;Ginsburg,1966