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The “Rule of One”

The Rule of One states that when the defenders hold only one trump that is higher than yours (as declarer), do not waste two of your trumps to get rid of it - it will win a trick anyway.

South Deals
None Vul
K 6 4
K 4 2
9 7 6 4
A 3 2
10 7
J 9
K J 8 5 3
K Q 10 6
W   E
Q J 5
10 8 7 5
Q 10
J 8 5 4
A 9 8 3 2
A Q 6 3
A 2
9 7
West North East South
      1 ♠
Pass 2  Pass 2 
Pass 3 ♠ Pass 4 ♠
Pass Pass Pass


Note the bidding - North's 2  bid is more of a waiting bid than anything else - allowing South to make a low-level rebid. When he introduces s, North is worth a jump-preference for his first suit, ♠s, knowing South will realise that he only holds three-card support because he did not support ♠s immediately.

West led ♣ K and declarer won ♣ A and cashed ♠ K and ♠ A. With both opponents following, there was just one trump outstanding, ♠ Q. But it would be grave folly to lead a third trump.

Declarer is actually 100% certain of his contract at this point. All he needs to do is play through his s. If they split 3-3 then the fourth is a winner by virtue of its length. But a 4-2 split will cause no problems either. If the hand with two s also has ♠ Q, he is welcome to trump the third top with it, as declarer will now be able to trump his losing fourth with dummy's remaining trump. In actuality declarer is able to lead out all four s, peacefully trumping the fourth in dummy.

THE RULE OF ONE: Leave the master trump outstanding.

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