/**
* Begin nesting predicates
*
* @return Predicate
*/
public function nest()
{
$predicateSet = new Predicate();
$predicateSet->setUnnest($this);
$this->addPredicate($predicateSet, $this->nextPredicateCombineOperator ?: $this->defaultCombination);
$this->nextPredicateCombineOperator = null;
return $predicateSet;
}