Flip-Pushdown Automata With K Pushdown Reversals And E0l Systems Are Incomparable

We prove that any propagating EOL system cannot generate the language [w#w vertical bar w is an element of {0, 1}*}. This result, together with some known ones, enables us to conclude that the flip-pushdown automata with k pushdown reversals, i.e., the pushdown automata with the ability to flip the pushdown, and EOL systems are incomparable. This result solves an open problem stated by Holzer and Kutrib in 2003. (C) 2014 Elsevier B.V. All rights reserved.