public function instantiate(NameSource $name_source)
 {
     $l = $this->_l->instantiate($name_source);
     $r = $this->_r->instantiate($l["name_source"]);
     $collector = Collector::combineCollectors($l["collector"], $r["collector"]);
     return array("builder" => new CombinedBuilder($l["builder"], $r["builder"]), "collector" => $collector, "name_source" => $r["name_source"]);
 }