Mohave Daily Miner – 18 Ene 1985
North dealer. North-South vulnerable.
Opening lead: 
6.
When you play against a good pair and they voluntarily bid a slam, only rarely will they finish with less than eleven tricks. You will, therefore seldom fatten your pocketbook much by doubling when they bid a slam. You may net an extra 50 or 100 extra points, but that’s no big deal.
But if the effect of doubling them is that you chase the opponents out of a contract they can’t make into one that they can make, you become responsible for a major catastrophe induced by the double. So, if the enemy bid and make six clubs doubled, vulnerable, they score 1,740 points. If they go down one undisturbed, they lose 100 points; if they go down one doubled, they lose 200 points.
Therefore, it simply doesn’t pay in the long run to double the enemy in a slam unless you have them lashed to the mast whichever way they turn.
Furthermore, an injudicious double frequently helps declarer during the play: for it alerts him to the location of the missing cards and he may, as a result, make the slam in a hand where he would fail in the absence of the double.
There is one important exception to the principle of not doubling slams. A double by the player not on lead may be used to alert his partner that the slam can be defeated by an abnormial lead. The slam-doubling convention applies to the type of hand on view. It is not difficult for West to deduce, considering his spade length and North’s spade bid; that the abnormal lead East is suggesting by his double is a spade. That is the only lead that can defeat the slam.