my $xpc = XML::LibXML::XPathContext->new($doc);
$xpc->registerNs('p', 'http://www.crtp.it');
$xpc->registerNs('p2', 'http://www.crpt.com');
my $result = $xpc->findnodes("/p2:login/p:utenti[p:email='$email' and p:password='$digestpass']/p:admin");

##</code><code>##

my $result = $doc->findnodes(qq{
/*[ local-name()="login" and namespace-uri()="http://www.crpt.com" ]
/*[ local-name()="utenti" and namespace-uri()="http://www.crtp.it" ]
  [
    *[ local-name()="email" and namespace-uri()="http://www.crtp.it" and string(node())="$email" ]
    and
    *[ local-name()="password" and namespace-uri()="http://www.crtp.it" and string(node())="$digestpass" ]
  ]
/*[ local-name()="admin" and namespace-uri()="http://www.crtp.it" ]
});