我在互联网上搜索过，大多数人只是说上下文无关语言对于联合、连接、反转和 Kleene Star 是封闭的。它们是否也因设置差异而关闭？
set discrete-mathematics context-free-grammar formal-languages context-free-language
context-free-grammar ×1
context-free-language ×1
discrete-mathematics ×1
formal-languages ×1
set ×1