1. Lower bounds on space complexity for context-free recognition;Alt;Acta Inform.,1979
2. Lower bounds for the space complexity of context-free recognition;Alt,1976
3. V. Geffert, Tally versions of Savitch's and Immermann-Szelepcsényi theorems for sublogarithmic space, SIAM J. Comput., to appear.
4. Formal Languages and their Relation to Automata;Hopcroft,1969
5. Nondeterministic space is closed under complementation;Immermann;SIAM J. Comput.,1988