规则Rules：
标准数独基础上，如果箭头格为A，箭头指向的方向上一定有A。
Classic rules applied. Additionally, if the arrow cell is A, then the direction the arrow points must contain A.
◆例题 Example
◆在线涂鸦 Draw it Online
◆在线做 Do it by CTC
◆在线做 Do it by Penpa
设计主题Theme：汉字 因
