文摘
In this paper we consider three restricted variants of P systems with active membranes: (1) P systems using send-out communication rules only, (2) P systems using elementary membrane division and dissolution rules only, and (3) polarizationless P systems using dissolution and unit evolution rules only. We show that every problem in \(\mathbf {P}\) can be solved with uniform families of any of these variants using reasonably weak uniformity conditions. This, using known results on the upper bound of the computational power of variants (1) and (3) yields new characterizations of the class \(\mathbf {P}\). In the case of variant (2) we provide a further characterization of \(\mathbf {P}\) by giving a semantic restriction on the computations of P systems of this variant.