 Beckett was unable to find a Beckett–Gray code for his play, and indeed, an exhaustive listing of all possible sequences reveals that no such code exists for "n" = 4.It is known today that such codes do exist for "n" = 2, 5, 6, 7, and 8, and do not exist for "n" = 3 or 4.An example of an 8-bit Beckett–Gray code can be found in Donald Knuth's "Art of Computer Programming".