Minimal cooperation in polarizationless P systems with active membranes

P systems with active membranes is a well developed framework in the eld of Membrane Computing. Using evolution, communication, dissolution and division rules, we know that some kinds of problems can be solved by those systems, but taking into account which ingredients are used. All these rules are inspired by the behavior of living cells, who \compute" with their proteins in order to obtain energy, create components, send information to other cells, kill themselves (in a process called apoptosis), and so on. But there are other behaviors not captured in this framework. As mitosis is simulated by division rules (for elementary and non-elementary membranes), meiosis, that is, membrane ssion inspiration is captured in separation rules. It di ers from the rst in the sense of duplication of the objects (that is, in division rules, we duplicate the objects not involved in the rule, meanwhile in separation rules we divide the content of the original membrane into the new membranes created). Evolution rules simulate the transformation of components in membranes, but it is well known that elements interact with another ones in order to obtain new components. Cooperation in evolution rules is considered. More speci cally, minimal cooperation (in the sense that only two objects can interact in order to create one or two objects