Another Compound

Dlr E
Vul NS
IMPs

	♠ A 8 7 3
	♥ A Q 10 2
	♦ K 7 6 5
	♣ 6
	♠ K 2
	♥ K J 8 7
	♦ A J
	♣ A K Q 10 4

West	North	East	South
		3♣	3NT
5♣	6♣	Pass	7NT
All Pass

♣3 led. RHO puts up the Jack. How do you play?

FWIW, RHO is an honest customer, LHO not so much. You can confirm this by playing another club.

My line and further analysis is below.



I tested one more club and LHO pitched ♠4 (I pitched ♠3 from dummy). Then 4 rounds of hearts, LHO following up the line, while RHO pitched ♣7, ♠5, then ♦4.

There's definitely a squeeze available at this point, but I still haven't committed to which one to play for. ♠K drew the Jack from RHO and 6 from LHO. Now I can afford another club before making up my mind: LHO pitched ♠9 while RHO followed with the 5. This is the ending:


 

	♠ A 8
	♥
	♦ K 7 6
	♣
	♠ 2
	♥
	♦ A J
	♣ 10 4

RHO is down to a club stopper and 3 pointed cards. If he started with 4 spades (and so still has that suit stopped), LHO made a very tricky pitch from 3=4=5=1 at trick 2 (and again on the last trick). Not to mention that the aggressive 3♣ opening seems much more likely with 4 diamonds than 4 spades. So, I played a spade to the Ace, and when RHO showed out I claimed: he must pitch his diamond guard here, then ♦A, ♣10 squeezes LHO in diamonds and spades.

If I had thought that RHO guarded spades but not diamonds, then ♦K, ♦A, ♣10 would effect a similar squeeze.

Technically this was just a double squeeze (LHO guards spades, RHO guards clubs, both guard diamonds), but if RHO had started 3=1=3=6 it would have been a true compound (a Type-R Unrestricted).

How about the defense?

East is going to need to make 2 pitches on the hearts, and then declarer is going to need to guess which of the pointed suits East still guards. If, as on the actual hand, East pitches one from each suit, he'd better not have started 3=3 or declarer cannot go wrong. On the other hand, even though East has had to make 2 pitches, always pitching one from each reveals nothing about which suit started longer. If West also pitches one from each suit (he has to make 2 pitches on clubs), declarer faces a straight guess (ignoring the auction), even though this is (or at least looks like) an unrestricted compound.

In compensation, if East did start 3=3, he must pitch 2 from a single suit, and declarer will almost always go right by playing that suit to now be unguarded. When East is actually pitching 2 from a 5 card suit (which he should do instead of 1 from each), declarer should normally go wrong (3-3 vs 5-1 is 25:3 a priori, though knowing an opponent's preempting style might be enough to overcome that).

I guess when the layout is such that it's not a true compound, just a double, that the position-tightening does not actually put anyone under pressure and so it makes sense that proper discarding reveals virtually nothing. There's always a double squeeze present, but it's more or less a toss up as to which to play for if both defenders are perfect. In contrast, when it is a true compound, East is squeezed twice and his discards are much more revealing, making it around 80% that declarer gets it right even against perfect defenders.

Obviously in practice a psuedo-squeeze is much more likely than this layout and West should be minimizing the chance of screwing that up.

Some minor technical points:

1. I should not have played a club at trick 2. RHO might not appreciate what is going on and if he pitches 2 clubs I'm spared any guess.

2. If I do play a club, I might as well pitch a heart. LHO might have trouble pitching from a 4 card holding in diamonds or spades. Also, I might as well play a 3rd (but not a 4th!). This gets more information from LHO early, without really helping RHO much if at all.

3. When crossing back to hand, I should probably use ♦A in case the ♦Q has been bared.

Finally, the ♦J was not strictly necessary, but it does help slightly in constraining the defense. Earlier I suggested that LHO pitching a spade early (and another later) from 3=4=5=1 would be tricky. This follows the general "principle" (technically this principle is false, but that's another post) of not waiting to the last possible moment to release a guard if you're squeeze. Since West is going to be squeezed in diamonds and spades later in the hand, if he anticipates this he has a good chance of leading declarer astray by pitching from his shorter suit early. However, thanks to the ♦J, he actually can't get away with pitching 2 diamonds (he started with Qxx). At double dummy the clash menace is irrelevant, but at single dummy it puts additional constraints on the defense and may make reading the position slightly easier.




The BBO record is here.