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Dlr: North ♠ A 8 7 2
Vul: Both A 5 3
A K 7 5
♣ 7 4
♠ K Q J 4 3
7
10 8 3 2
♣ A K Q

 

West North East South
1NT 3 3♠
Pass 4 Pass 4NT (1)
Pass 5♣ (2) Pass  6♠
All Pass

(1) Roman Key Card Blackwood
(2) Zero or three key cards
West leads the 4 against your spade slam. Plan your play.

Solution

When dummy came down, declarer was delighted: 12 tricks would always be there if the diamonds could be played for three tricks. After taking the opening lead with dummy’s A, declarer cashed the top three spades in his hand, East showing out. East played hearts to the first four tricks.
Declarer then played the three top clubs, throwing a diamond from dummy. East’s heart discard was a small problem, suggesting that diamonds might not break 3-2. A diamond was led towards the dummy in case West was void in the suit. After both defenders followed with low diamonds under the king, declarer could count East as having started with either 0=7=4=2 or 0=8=3=2.
Declarer cashed the *S*A, reducing everyone to four cards.
On the basis that West’s 4 was a singleton or from 4-2 doubleton, the only unknown was the location of the 2. If East had kept two hearts higher than the 2, he could have at most two diamonds remaining: if that were the case, declarer planned to continue with the A and another diamond, establishing the 10 as the 12th trick with the ♠4 as the entry to cash it.
If East had kept the equivalent of a singleton K or the K 2, declarer had a strategy in mind to cope: He would lead the 3 from dummy and discard a diamond from hand. As a result, either the 3 would win or the 5 would be established as a winner for a second diamond discard. So, no matter what East chose to do in such an ending, declarer would have made five trumps, two hearts, two diamonds and three clubs for a total of 12 tricks. The full deal:

Dlr: North ♠ A 8 7 2
Vul: Both A 5 3
A K 7 5
♣ 7 4
♠ 10 9 6 5 ♠ —
4 2 K Q J 10 9 8 6
4 Q J 9 6
♣ 10 9 6 5 3 2 ♣ J 8
♠ K Q J 4 3
7
10 8 3 2
♣ A K Q