SwissCross

A simple simulation consists of a square array of cells, each holding a number of grains of sand. Any pile containing more than 3 grains becomes unstable and sheds one grain to each of its four immediate neighbours. These cells may then themselves contain more than 3 grains and shed grains to their neighbours, and so on. The evolution of this system eventually terminates (with each cell holding at most 3 grains), and the result is independent of the order in which the redistribution process is carried out.