sub permute {
    return if $_[0] && $_[0] / length($_[0]) != int ($_[0] / length($_[0]));
    if (!length($_[1])) { print $_[0]." "; return; }
    for (0..length($_[1])-1) {
         permute($_[0].substr($_[1],$_,1), substr($_[1],0,$_).substr($_[1],$_+1));
    }
}