At the NABC in Philadelphia, Ethan Stein of Irvington, New York, asked me this: Does the computer app Deep Finesse ever make a mistake? I told him that a few bugs had been edited out over a decade ago, but I had not heard of anything recently.
Ethan said he was struggling to find out why Deep Finesse had claimed that no more than 11 tricks could be won on the deal shown. After some false starts, we left it TBD. The next day, Ethan cracked it … but why should I spoil your fun? Cover the South and East cards and defend against six hearts.
A spade lead is suicidal, while if you lead a diamond, declarer will discard a spade on the diamond king, finesse a club and ruff a club. On a heart lead, declarer wins in hand and leads a diamond, using the heart jack and the club jack to set up diamonds, and the club king to reach the long card.
A club lead is best, attacking the late entries to the diamonds. Declarer has to win with the jack and run hearts after unblocking the club king, reaching a five-card ending with A-x in both black suits and a diamond facing the spade Q-10 and three diamonds in dummy.
While it is true that West, who holds two spades and three diamonds, gets squeezed on the club ace in the five-card ending — forcing a diamond discard — dummy also gets squeezed! As declarer, you cannot pitch a spade from dummy, so you must discard a diamond. However, now West can win declarer’s diamond lead with the ace and exit in diamonds, eventually scoring a spade trick.
All things considered, that is a relatively unlikely combination of circumstances.