Thus for any sentence A {\displaystyle A} (simple or compound), the compound sentences ◻ A {\displaystyle \Box A} and ◊ A {\displaystyle \Diamond A} can be formed.
对于任何(简单的或复合的)句子 A，我们可以由此形成复合句子 ◻ A {\displaystyle \Box A} 和 ◊ A {\displaystyle \Diamond A} 。