v 0 0 0 v 1 0 0 v 1 1 0 v 0 1 0 v 0 0 1 v 1 0 1 v 1 1 1 v 0 1 1 f 1 2 3 4 f 5 6 7 8 l 1 5 l 2 6 l 3 7 l 4 8