sub odd {
    return 1   if  "1" eq $_[0];
    die "Can't test the oddness of anything but '1'.\n";
}

##</code><code>##

sub odd {
    my $num= shift @_;
    die "Out of range"   if  2**52 <= abs($num);
    return $num % 2;
}

sub odd {
    my $num= shift @_;
    die "Out of range"   if  1 != (1+$num)-$num;
    return $num % 2;
}