Prof. Tao himself links to the wikipedia article https://en.wikipedia.org/wiki/Common_knowledge_%28logic%29 https://en.wikipedia.org/wiki/Common_knowledge_%28lo

Prof. Tao himself links to the wikipedia article https://en.wikipedia.org/wiki/Common_knowledge_%28logic%29 https://en.wikipedia.org/wiki/Common_knowledge_%28logic%29 which uses this as an example for Common Logic.