if (getlastmod($potiersurl) == filemtime('PO_tiers.xml')) {
        logadd('No changes in PO tiers.');
        die();
    }
    else {
        logadd('PO tiers were updated.');
        $x->asXML('PO_tiers.xml');
        touch('PO_tiers.xml', getlastmod($potiersurl));
        logadd('New PO_tiers.xml loaded');
    }