Two Universality Results for (Mem)Brane Systems

Abstract

We prove that P systems with mate and drip operations and using at most
\nfive membranes during any step of a computation are universal. This improves a recent
\nsimilar result from, where eleven membranes are used. The proof of this result has the
\n"drawback" that the output of a computation is obtained on an inner membrane of the
\nsystem. A universality proof is then given for the case when the result of a computation is
\nfound on the skin membrane (on its external side, hence "visible" from the environment),
\nbut in this case we use one more membrane, as well as another basic brane operation
\nexo; moreover, the operations are now of the projective type, as introduced in.