P systems with symport/antiport rules of a minimal size (only one object passes in any direction in a communication step) have been recently proved to be computationally universal. The result originally reported in [2] has been subsequently improved in [6] by showing that six membranes suffice. In [6] it has been also conjectured that at least one membrane can be saved. Here we prove that conjecture: P systems with five membranes and symport/antiport rules of a minimal size are computationally complete. The optimality of this result remains open.
['Francesco Bernardini', 'Andrei Paun']
Universality of minimal symport/antiport: Five membranes suffice