[ahydra]

Partner wanted to discuss this hand from the Swiss Teams, so I ran it through Deep Finesse... and ended up having a lot of fun.

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Partner led the ♥5 against 3NT - would you find the double-dummy defence?

Spoiler

At trick 1, South must lead a heart (other than the 10) to beat it by 2 tricks. A spade beats it 1 trick, but the H10 lead (or a minor-suit card) lets it make.

The first trick goes 5, Q, 7, 6. Now dummy plays two rounds of diamonds and South wins the Ace. South must now make the key play of the heart KING!! Would you believe it! Then he throws spades away on the diamonds, and eventually cashes lots of hearts to beat the contract two tricks.

If instead South plays a small heart to partner's Jack at trick 4, declarer must DUCK so now the defence can't knock out the HA safely.

On a spade lead, the play is even crazier. First, North must overtake the SJ with the SK immediately and play hearts, otherwise the contract will make. Suppose he does not - declarer wins the Q, knocks out the DA, then South must continue with another spade and declarer must win the SA immediately.

Assuming you get all that right, declarer now can't run his diamonds!! If he does then, assuming South holds on to all his spades, eventually the defence (having taken the SK, DA, CA) defeat the contract by making the HK and the magical two of spades! But if declarer instead sets up clubs, he can get across to dummy with the DJ and cash the 9th trick, the CK.

ahydra