Occasionally when you and your partner are in the midst of doing some fine tuned slam bidding, venturesome opponents decide to interfere. Usually they are attempting to find a sacrifice that will prove profitable versus your likely slam, but, in addition, they are making your bidding more difficult. These types of actions occur at high levels and at favorable (for them) vulnerability. While their attempts may prove fatal for them (bridgewise that is), it’s also a very real imposition to your positive slam bidding. All players at the table need to attempt to calculate possible damages and assess the advantages and disadvantages of continuing to bid and/or of deciding to defend.
Example: Dealer: North Vul: None
 9  A863  AK83  QJ109 |
||
| QJ742 9754 9652 – |
AK108653 J 1074 62 |
|
| KQ102 QJ AK87543 |
| North | East | South | West |
| 1 |
3 |
4NT | 5 |
Here West has decided that a sacrifice is in order so bids 5 ’s. Now North has a dilemma. He can double and find out later that E-W were down only two for a paltry score of 300 points. Or he can bid on to slam in clubs for a hopeful score of 920. Before North decides to double in situations similar to this, he would like to be certain that the result of this double is best that N-S can do on the board. In the example above, the double would serve no purpose as North is anything but certain and South would have to assume that the double by his partner is a penalty double and thus would subsequently pass.
On the other hand, if North would like to continue to explore for a slam in clubs, the problem is how to show his Aces with the traditional method being to pass with no Aces or bid the cheapest suit possible that contains an Ace, and so on up the line. This method is quite obvious lacking so bridge players have devised their own conventional means for showing Aces. These conventions and/or methods are explained below. They are not complicated or involved with a lot of memorization, but bridge players do need to choose one convention for such situations.
DEPO stands for Double Even-Pass Odd. Using this convention, a double shows an even number of Aces ….zero, two or four. Pass shows an odd number of Aces… one or three. Using DEPO in the above example North would double to show an Even Number of Aces.
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