Flip-pushdown automata with k pushdown reversals and E0L systems are incomparable

We prove that any propagating E0L system cannot generate the language {w#w|w∈{0,1}⁎}{w#w|w∈{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 E0L systems are incomparable. This result solves an open problem stated by Holzer and Kutrib in 2003.