An item of information of data in a very game is common grasp ledge if all of the players realize it (it is mutual grasp ledge) and every one of the players grasp that each one different players realize it and every one different players know that each one different players know that each one different players realize it, and so on. this can be rather more than merely saying that one thing is thought by all, however conjointly implies that the actual fact that it's known is additionally known by all, etc. take into account an easy example of 2 allied armies situated on opposite hilltops waiting to attack their foe. Neither commander can attack unless he's positive that the opposite can attack at precisely the same time. the primary commander sends a messenger to the opposite hilltop with the message "I conceive to attack within the morning." The messenger's journey is perilous and he might die on the thanks to delivering the message. If he gets to the opposite hilltop and informs the opposite commander - will we have a tendency to make certain that each can attack within the morning? Note that each commanders currently grasp the message, however the primary cannot be positive that the second got the message. Thus, common information implies not solely that each grasp some piece of knowledge, however may be completely assured that the remainder no it, which the remainder grasp that we all know it, and so on.