fundamentals HPP Gas

This 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:
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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.