规则Rules：
标准数独基础上，提示表示这一方向上，此数字之前有更大的数字。
Classic rules applied. Additionally, clue indicate an larger number exists before it.
*规则有修改过，以此版本为准。The rules are different with rules in the link. This version shall prevail.
◆在线做 Do it by CTC
◆在线做 Do it by Penpa
