Two Universality Results for (Mem)Brane Systems

Abstract

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