fundamentals HPP GasThis automaton does not use the known neighbourhood, but brackets 4 cells together (near the border 1 and 2 cells too).
The following table shows the transition rules. Per rotation you get all possibilities.
In the next generation the bracket together is shifted by 1 row and 1 column.
The procedure looks like this:
This process is called Margolus neighbourhood.
More automata with this neighboarhood you'll find in mode Margolus!
More information you'll find in the related Wikipedia article lattice gas automaton.