use CGI;
                                                                                
my %symbols;
                                                                                
for my $foo ( keys %main:: )
{
   $symbols{$foo} = 1;
}
                                                                                
CGI::import 'CGI',':form';
                                                                                
for my $foo ( grep !exists $symbols{$_} , keys %main:: )
{
   print $foo,"\n";
}