Rule structure [for network systems]

For depth 1, the possible results from NeighborNumbers are {1} and {2}. For depth 2, they are {1, 1}, {1, 2}, {2, 1}, {2, 2}, {2, 3} and {2, 4}. In general, each successive element in a list from NeighborNumbers cannot be more than twice the previous element.