my $addon = '';
if ( exists( $Data{gen}{$randomkey}{bk} ) or
     exists( $Data{gen}{$randomkey}{pg} ))
{
    $addon = $Data{gen}{$randomkey}{bk} || 'Monstrous Manual';
    $addon .= ", page $Data{gen}{$randomkey}{pg}"
        if ( exists( $Data{gen}{$randomkey}{pg} ));
}
$output .= " ($addon)" if ( $addon );