Editing P system (section)

====Non-deterministic application====
The order of rule application is chosen at random. Rule application order can have a significant effect on which rules may be applied at any given time, and the outcome of a step of execution.

Consider a membrane containing only a single "a" symbol, and the two rules a → ab and a → aδ. As both rules rely on an “a” symbol being present, of which there is only one, the first step of computation will allow either the first or second rule to be applied, but not both. The two possible results of this step are very different:
#The membrane carries over to the next step of the computation with both an "a" symbol and a "b" symbol present, and again one of the two rules is randomly assigned to the "a" symbol.
#The membrane dissolves and a single "a" symbol is passed out to the containing membrane.