#N Gray counter
#C A period 4 oscillator.
#C http://www.conwaylife.com/wiki/index.php?title=Gray_counter
x = 13, y = 9, rule = B3/S23
6bo6b$5bobo5b$4bobobo4b$bo2bo3bo2bob$obobo3bobobo$bo2bo3bo2bob$4bobobo
4b$5bobo5b$6bo!