UNAMBIGUOUS SIMULATIONS OF AUXILIARY PUSHDOWN-AUTOMATA AND CIRCUITS

A simulation 'free of cost' of polynomially ambiguity bounded AuxPDAs by unambiguous ones is given. From this it follows that context free languages (CFLs) of polynomial ambiguity can be recognized as efficiently by unambiguous auxiliary pushdown automata (AuxPDAs) as unambiguous CFLs (UCFLs). Furthermore, a first nontrivial upper bound for a circuit class defined by Lange and its closure under complementation are indicated. Finally, normal forms for AuxPDAs are investigated; inter alia it is shown that several kinds of AuxPDAs can be made oblivious, i.e., the movements of all heads are independent from the input.