In the game of bridge, we are required to disclose the agreements on our bidding and defense playing. What will happen if this requirement is removed, such that the game is played with secret agreements that we don't need to disclose the meaning of our bids and defense playing to the opponents? I think it will be more interesting as without disclosure, the bidding systems will be designed in a way such that the communication can be done without opponents' guessing the meaning, while disrupting their bidding as possible. Also, it will be harder to deduce the opponent's holdings from the bidding, when all the meanings are kept secret, so you need to use your own communications, and make a guess on their biddings.