public static function compare($left, $right){
		if($left->a != $right->a) return $left->a <=> $right->a;
		if($left->b != $right->b) return $left->b <=> $right->b;
		if($left->c != $right->c) return $left->c <=> $right->c;
		if($left->i < 0 || $right->i < 0) return 0;
		return $left->i <=> $right->i;
	}