? rex([
>    0,  1,  2,  4,  6,  7,  8, 11, 12, 14,
>    15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
>    25, 27, 28, 29, 30, 31, 32, 33, 35, 36,
>    37, 38, 39])
# value: "0-2,4,6-8,11,12,14-25,27-33,35-39"