!Name: Gray counter
!A period 4 oscillator.
!https://www.conwaylife.com/wiki/index.php?title=Gray_counter
......O
.....O.O
....O.O.O
.O..O...O..O
O.O.O...O.O.O
.O..O...O..O
....O.O.O
.....O.O
......O