function pop(){
		if( ! $this->length ){
			return null;
		}
		if( --$this->length <= 0 ){
			$this->length = 0;
			$this->p = null;
		}
		else {
			$this->p = 0;
		}
		$Node = array_pop( $this->children );
		$Node->pidx = null;
		$Node->depth = 0;
		return $Node;
	}