sub show_these {
    my ($dr,$show,$sort) = @_;
    my $output;
    if (!$sort) { $sort = sub {
        my $id = shift;
        return sort { $a <=> $b } keys %{$dr}
                }
    }
    my (@order) = $sort->($dr);
    for my $row (@order) {
        for (@{$show}) {
            next if !$dr->{$row}{$_};
            $output .= qq!$_ = $dr->{$row}{$_} !;
        }
        $output .= "\n";
    }        
    return $output;
}