So again, they both know that someone in the room has a pink hat on their head: it is mutual knowledge that there's a pink hat in the room.

但是他们都知道,至少有一个人戴着粉色帽子,至少有一顶粉色帽子是相互知识

耶鲁公开课 - 博弈论课程节选

Mutual knowledge doesn't imply common knowledge.

相互知识并不是公共知识

耶鲁公开课 - 博弈论课程节选