Two group of players, player 1, and player 2 compete in a hockey game every week. There are many players but every week one player from each group fights against one another. The winning group receives 6000, while the losing group gets nothing. Against the contract, the groups discuss to split prize money in half. If one group cheats, the other group will fight hard forever (grim trigger) leaving each with an expected payoff of $2,000 due to injury expenses. What must be true of (the same for each group) for this to work