[11.1、union可以合并集合（相加）](11.1%E3%80%81union%E5%8F%AF%E4%BB%A5%E5%90%88%E5%B9%B6%E9%9B%86%E5%90%88%EF%BC%88%E7%9B%B8%E5%8A%A0%EF%BC%89.md)