Sunday, January 15, 2012

Looks simple

It's the first hand of the evening at one of last week's STAC games (only we are vulnerable). After partner opens 3 in second seat, we find ourselves in 3NT with no opposition bidding. The lead is the 2 (fourth best) and this is what we see:

9 4 2
10 7
A Q 10 9 8 6 3
My hand
A K Q 8
Q J 3
5 2
K Q 10 3

The opponents clear the hearts, we lead a small diamond, LHO follows with the four and it's decision time. Well, the first thing you notice about the dummy is that it's totally entryless outside diamonds (it's a great preempt, isn't it?).  The defenders have taken two tricks already and have a heart and a club to cash. So, if we're playing IMPs, we need to bring in the entire suit, so must finesse the Q to give us the best chance (about 26%) of making. At first glance, you might think that the chance of making is 50% but in practice, if we finesse the Q and it wins, we must also have a 2-2 split or see the J drop on our right.  Though even then, there's the chance of a dastardly defender deliberately throwing us off holding KJ.

In a diamond contract, there are at least 9 tricks so in effect we aren't competing with the declarers in diamonds. In any case, of 17 tables, only two played in diamonds. So, how do we maximize the number of tricks we will take, keeping in mind that the number may well be less than nine? Finesse the 10 (8 or 9) on the first round, in keeping with the Principle of Least Commitment. This play either breaks even or loses a trick to the Q play when the honors are split. But it enjoys a big win in the case where KJx is on our left and x is on our right (since we have no outside entries to dummy this layout will kill the suit stone dead if we finesse the Q). The 10 play also has a minor win in the unfortunate case where KJxx are all on our left, although this will not be a big comfort at the time. Nothing works of course when KJ are guarded on the right. See the table below for the details.

Layout Cases Probability Q tricks T tricks Q expect T expect
KJxx - 1 4.78% 2 3 0.096 0.143
KJx – x 2 12.44% 2 7 0.249 0.871
Kxx – J 1 6.22% 7 6 0.435 0.373
Kx – Jx 2 13.56% 7 6 0.949 0.814
Jxx – K 1 6.22% 6 6 0.373 0.373
Jx – Kx 2 13.56% 6 6 0.814 0.814
xx – KJ 1 6.78% 6 6 0.407 0.407
x – KJx 2 12.44% 1 1 0.124 0.124
Total 12 76.00% 53 61 4.536 5.157

4.42 5.08

When the "books" take a look at a suit like this, they assume that entries are available wherever needed.  However, with the excellent SuitPlay program by Jeroen Warmerdam, you can explicitly tell it how many entries accompany the suit, etc.

Since everything must be decided on the two leads towards dummy, we effectively have four realistic lines of play: Q or 10 on the first lead, A or the remaining honor on the second.  My analysis assumes that we will always guess right on the second lead but this will be easier sometimes than at other times.  In particular, if the Q won on the first trick, the Kx-Jx layout will be picked up easily.  But if the Q loses to the K, and LHO plays small to the second trick, we won't know whether he started with xx or Jxx.  Against most defenders, the 10 play may make the second guess easier because players tend to win as economically as possible. So, in a way, playing that 10 first is something of a safety play.

The best matchpoint line, starting with a finesse of the 10 and the one which I happened to choose at the table, did not give me the best chance of making the contract.  But it did give me the maximum expectation of diamond tricks.  As it happens, I lost the first trick to the J.  I was fortunate in that the defender who won the last heart trick didn't have the club ace and chose to lead a spade.  I therefore made my contract exactly.  This was worth only 5.5 out of 16 (approx 33%), however.  I shouldn't really be surprised.  At a club pairs, players perceive a premium on making contracts (and don't typically worry about minimizing the set). Perhaps in the Blue Ribbons I'd have had more company.

The table above has two columns each for the Q and the T plays.  The first is the number of tricks yielded.  The second is the expectation of tricks (the number times the probability).  By summing the expectations, we can compare the overall expectations of the two lines.  However, we poor humans cannot do these kinds of calculations at the table in practice (Chthonic would have no problem of course).  There's another, simplified, method of comparing the lines that Eric Rodwell describes in The Rodwell Files.  He suggests assuming that all possible layouts are equally likely.  This isn't quite accurate of course because, due to considerations of vacant places, KJ74 in one hand is not as likely as, say, KJ opposite 74.  That's because once the K and J have been "placed" in one hand, there are two fewer vacant places in that hand to take the 7, and if the 7 does go with the KJ, there are now three fewer vacant places to accommodate the 4 in the same hand.  However, to a first approximation, we can assume equal likelihood of each layout.  When there are n outstanding cards, there are 2^n possible layouts.  In this case, four missing cards so there are 16 possible layouts.

Once LHO plays a small card (the 7 or 4 in this case) to the first diamond lead, we can immediately eliminate four of the 16 cases. In the table above, the bottom row, labeled Approx, shows the expectations when we use this simplified method of calculation.  The two approximate values are 53/12 and 61/12.  As you can see, the numbers are very close to the accurate values.

However, for a complex situation like this one, even this amount of calculation is too much.  That's why I find myself frequently falling back on the principle of least commitment.


  1. I'm surprised at several levels.

    First, I consider the responder hand a clear pass of a 3D opening: can't reasonably expect to run diamonds and there are very few tricks with only a diamond trick or two. THAT is the difference I would expect most to see in the Blue Ribbon Pairs: better bidding judgment.

    Second, is there a way for the defense to better communicate, so that a club can be cashed along the way? There seem to be a number of possibilities, of which the easiest might be for opening leader's third round lead of hearts to be a suit preference card; that is, for example, from, say, K852, to return the 5 when holding a high club and the 8 when holding a high spade: what else can the meaning of those spots be once third hand has returned an original fourth best card at Trick 2? Another possibility, possibly not practical since declarer's ownership of two heart honors might not be discernible, is to allow declarer to win the second round of hearts and not the third round, thus retaining flexibility as to who is on lead when.

    Third, does the chart have errors?

    a) If suit is Jx/Kx, then don't the two plays each produce six tricks, and yet chart says that playing the ten produces seven tricks?

    b) If a first round finesse of Q loses to the king, what is preferred play on second round when LHO follows small? Showing Jxx/K split as six tricks implies that my second round play is the ten, but then showing xx/KJ split as six tricks implies that my second round play is the ace. Is that inconsistent?

    Btw, how does the fact that opening leader has led from a four card suit (suggesting owning no five card suit) affect my diamond play choices, by presenting some inference that he might have length in diamonds? That factor might tip matters in favor of the deep diamond finesse; not at all sure of that.

    At the table, I am sure I would not bid 3NT, but if I bid 3NT, my inclination -- of which I am not totally comfortable -- is to hope for Kx onside.

  2. Interesting points, Jeff. First, you are indeed correct about the table - I will fix it. Second, I did edit some stuff out because it was so long - my original did cover the suit preference possibilities in the heart suit.
    I also thought I had mentioned that I was assuming a perfect guess on the second round of diamonds - seems I edited that out too, though I realize that it won't always be obvious.
    Now we come to the real meat: your suggestion that in the Blue Ribbons, more people with my hand would pass 3D. We can never know for sure, but 15 out of 17 players at the club nevertheless ended up in 3NT. I personally felt it was a close decision but came out in favor of the game bid.
    I'm not sure that there's much to go on when LHO leads his fourth-best heart. That gives him 9 other cards in the other suits. I don't think it materially suggests length in diamonds but if it did, finessing the T on the first round would be slightly more strongly indicated.

  3. I am not sure exactly how experts would think about the possible effect of LHO having led from a four card suit on his diamond length ... but it is possible that an analysis might progress something as follows:

    Leading from an unbid four card suit suggests not owning an unbid five card suit. Having chosen one unbid four card suit suggests not owning another unbid four card suit (i.e., restricted choice). Thus distribution might be 3=4=3=3 or 4/4 in the red suits.

    I really don't know how far to read that (expecially since the lead was in our weakest major), but perhaps that is enough of an inference that LHO has enough diamond length to cause declarer to choose to finesse the DT on first round.

    As far as bidding 3NT or not, I don't doubt for one moment that the point counters at the club bid 3NT, but this is a hand where I would depart from the club field and expect to win mps. Not that 3NT bid is hopeless -- it is far from that -- but I surely feel that it is much more likely to convert a plus in a diamond partial into a minus as a game shot. Imagine the chances, for example, should partner's diamonds be something like KQJxxxx where a simple one round holdup of ace might be sufficient to torpedo the contract, leaving us with one diamond trick at notrump but six diamond tricks at diamonds.

    Ah, this is what makes this favored pastime so much fun.

    Thanks, as always, for taking the time to share the blog entry.

  4. You actually make it seem so easy with your presentation but I find this matter to be actually something which I think I would never understand. It seems too complex and extremely broad for me. I'm looking forward for your next post, I will try to get the hang of it!