|♠||A Q 7 3 2|
|♥||A Q 6|
|♣||K 10 7|
|♥||K 7 5 4 3|
|♦||8 7 6 4 3|
|♣||A 9 4|
The South hand was given to me as a "pure bidding problem", but this turned out to be a very interesting play hand. At IMPs, would you overcall after 1♦ on your right? Does it matter whether partner is a passed hand or not, or what the colors are?
FWIW, I think I would basically always overcall. LHO makes a negative double, and you wind up in 4♥.
Anyway, say you receive the lead of the stiff ♦K. RHO is 4=2=5=2 with ♠K and a club honor. Would you rather play or defend?
Here's one way to make on a guard squeeze with a delayed duck element: they play a trump at trick 2, you win in dummy, play another diamond, they play another trump. Now ruff a spade, ruff a diamond, ruff a spade, draw the last trump (pitching a spade) to come down to:
|♣||K 10 7|
|♣||A 9 4|
RHO must keep 2 spades or the queen is good. If he bares his club honor, his partner is exposed to a finesse, so he must be down to one diamond. Duck a diamond (the 8, of course) and you have the rest.
Since you're out of trumps, the ♠A is a key card: you need to hold that to keep control of the suit lest RHO come down to one diamond but be able to cash the SK when thrown in.
You also can't rectify the count in any way since every card in dummy is busy.
I have not checked with deep finesse, but I believe the defense can break this up. How? Answer below...
The hint is in the position requirements I pointed out. One approach is to attack the ♠A: after winning trick one, LHO can lead a spade. You play *low* and ruff, and play a 2nd diamond. If RHO wins this, there's not much he can do except play a red card which puts declarer in control of reaching the desired end position. But, what if LHO ruffs the 2nd diamond to lead another spade? Not good enough: declarer can ruff in hand, ruff a diamond, and overtake a trump to get back to hand and play the last trump.
So that fails. What about rectifying the count for declarer? By playing trumps twice, the defense can eliminate dummy's trump winners. Now when declarer goes to ruff a diamond, LHO can ruff in front of dummy for the defense's third trick. This breaks up the squeeze position above: declarer can still arrange to ruff a diamond but then dummy is squeezed before RHO.
However, it looks like declarer has another resource: LHO can't break the club suit and so must play a spade when in with his last trump. Declarer ruffs that, ruffs a diamond, ruffs a 3rd spade and now dummy is good.
But why can't LHO break the club suit? Declarer had to pitch one on the ruffed 3rd diamond, so in fact LHO could break clubs, and declarer is an entry shy.
Maybe declarer can counter this by arranging to ruff 2 spades before playing the 3rd diamond? Now the defense declines to ruff, and declarer has only the ♣A as reentry. But, that card is also essential to the squeeze position as it gives force to the delayed duck menace.
So, actually, in the end I think the defense can survive with an unusual ruff in front of dummy to squeeze dummy play.