function remove_at( $i ){
		$Child = $this->children[$i];
		$Child->pidx = null;
		$Child->depth = 0;
		array_splice( $this->children, $i, 1 );
		if( ! --$this->length ){
			$this->p = null;
		}
		else {
			$this->p = 0;
		}
		return $Child;
	}