Abstract
In [3] a variant of the computation model introduced by Gh. Păun in [1] is considered: membrane systems with external output, which were proven to be universal, in the sense that they are able to generate all Parikh images of recursively enumerable languages. Here we give another proof of the universality of this model. The proof is carried out associating to each deterministic Turing machine a P system with external output that simulates its running. Thus, although we work with symbol-objects, we get strings as a result of computations, and in this way we generate directly all recursively enumerable languages, instead of their images through Parikh mapping, as it is done in [3].