Evolution of elementary <a href="https://en.wikipedia.org/wiki/cellular_automaton" class="extiw" title="w:cellular automaton">CA</a> rule 18 and its <a href="https://en.wikipedia.org/wiki/second_order_cellular_automaton" class="extiw" title="w:second order cellular automaton">second order</a> counterpart from the same initial state.  Time runs downwards. Note the up/down asymmetric triangles formed by the nonreversible rule.
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