https://www.wischina.org/mazes-variables-and-clones-%e8%bf%b7%e5%ae%ab%ef%bc%8c%e5%8f%98%e9%87%8f%e5%92%8c%e5%85%8b%e9%9a%86/
Mazes, variables, and clones 迷宫,变量和克隆