After visiting our dear friend Blackwood in the last edition of Slams, we'll now have a look at control cue-bids.
It is really important to not be in a slam when the opponents can cash the Ace-King of a suit right away. That's the purpose of showing controls.
Having a control in a suit means the opening leader can't cash two quick tricks in the suit. Therefore there are 4 possible controls: an Ace, a King, a singleton or a void.