## Example taken from Python Reference Manual
##   Beautiful illustration of the logic behind
##   Pythonic splices.
def perm(l):
    """Compute the list of all permutations of l"""
    if len(l) <= 1:
        return [l]
    r = []
    for i in range(len(l)):
        # s = l with the ith element skipped.
        s = l[:i] + l[i+1:]
        p = perm(s)
        for x in p:
            # l[i:1+1]: singleton list onctianing i-th element
            r.append(l[i:i+1] + x)
    return r