Sunday, 4 March 2007

DBT10: Breaking Homogeneity

Some systems have bids which are explicitly defined as multi-way bids. Perhaps the archetypal example of a multi-way opening bid is the "Swedish" 1C opening, which shows either a weak balanced hand (11-13 HCP, say), or a strong hand of any shape (typically played as 17+ HCP). Natural systems do not use this sort of bid; however, many opening bids still contain a wide variety of possible hand types. For example, playing strong NT and 4-card majors, a 1H opening could be anything from a minimum balanced hand to a very strong 1- or 2-suiter. Clearly these are very different hand types, so the bid can be thought of as a multi-way bid in much the same way as the Swedish 1C is. The only difference is that the hand types in the natural bid are not separated by such a clear dividing line.

In either case, the important thing is to make sure that the various possible hand types go well together.

The One-Bid-Or-Two principle is very relevant here. If opener has a pure two-bid hand, then he will be able to reveal which hand type he has with his rebid. But if he has a one-bid hand, he may be unable to add anything to the initial description except to deny a hand suitable for taking a second bid. So, although responder's bids must cater for all the possible hand types opener can have, it is opener's one-bid hands which you need to be most concerned about. The opening bid must provide sufficiently good information about the one-bid hands that responder will know what to do. This does not necessarily mean that responder must be able to place the contract immediately, but he must at least be able to control the auction.

The easiest way to do this is to make the one-bid hands homogeneous. That is, while the opening bid as a whole may be a multi-way bid with a variety of different options, it is a good idea for all the one-bid hands to be covered by a single hand type - or perhaps by a small number of homogeneous hand types. The reason is simple: responder needs to know immediately what he should do opposite a one-bid hand, and a homogeneous opening bid is the best way of providing immediate information. All of the ideas about what makes a good homogeneous bid apply here.

For the two-bid hands, homogeneity is not so important: it is possible to have different rebids showing different hand types. The Swedish 1C opening is an excellent example of this. The one-bid hands are very homogeneous, consisting of a single hand type (11-13 HCP balanced), whereas there is much more variety in the two-bid hands: any shape is possible for the strong option. Many other well-designed multi-way bids work the same way: they have homogeneity in their one-bid hands, but it does not extend to their two-bid hands.

One problem with this sort of opening bid is a lack of flexibility. The different hand types are very clearly separated. So, if opener has a hand which is supposed to be treated as a two-bid hand, it is important to follow up by actually making the rebid which shows the hand. Unfortunately, as we know, not all hands are "pure" examples of one-bid or two-bid hands. A balanced 17-count is certainly not a pure two-bid hand. But if you open a two-way 1C, then this hand is treated as belonging to the strong variant. So if you are unlucky enough to have LHO overcall 2S, say, and responder raise to 3S, you will be in a difficult position. If you pass then partner will play you for a weak balanced hand, but there is no safety in making a free bid either. The lack of homogeneity between the different hand types is the problem here.

So this sort of bid works best when the "strong" hand types are genuine two-bid hands - as pure as possible. Ideally, they should either have overwhelming high-card strength (20+ HCP should ensure that the hand is a two-bid hand) or be very distributional - though in the latter case you need to be careful that you can actually describe the shape well with your rebid. (Single-suited hands are best for this.) In practice, most systems will have to allow some dubious hands into their strong options because of a lack of better places to put them, but clearly the strong option in our favourite example (17+ HCP, any shape) is already rather light, and anything weaker than this would be really asking for trouble.

Typically, if the one-bid hands are going to be homogeneous, this would mean that there is a particular hand type which responder will play opener to have until proven otherwise. We would call this the dominant hand type. Obviously the dominant hand type in the Swedish 1C opening is the weak balanced hand, but the term also makes sense for natural bids. For example, playing a standard 5-card major system, the dominant hand type in a 1S opening bid is a minimum hand with precisely 5 spades. More generally, the dominant hand type would usually be the most frequent one-bid hand type that opener can hold. We can state a general "homogeneity principle" in these terms:

All the one-bid hands in an opening bid should be as
close to the dominant hand type as possible.

The idea from a previous post that the "average" length (or strength) promised by an opening bid should be as close as possible to the minimum length (strength) is really just a special case of this. But we can now see that the average should be taken over only the one-bid hands. Two-bid hands do not need to be close to the dominant hand type, provided that they are pure two-bid hands. With an "in-between" hand you have a slight problem - it may work adequately well to treat them as two-bid hands, but it would also be helpful to have them be fairly similar to the homogeneous one-bid hands, in case the auction prevented opener from showing the precise hand type.

Bids which have a wide range of one-bid hands, or where there is no single dominant hand type, are much more problematic. But they do exist, with the most obvious example being the multi-2D opening bid. A multi-2D shows a weak hand with either hearts or spades (possibly with other strong options which are genuine two-bid hands). Although the strength promised is the same no matter which major suit is held, clearly in terms of distribution this is not a homogeneous bid. In a case like this, you have to find particular reasons why the bid "works" - why should responder be able to cater for both hand types at once? In general there is no guarantee that it will be possible.

There are a few reasons why the multi-2D is an effective bid. In particular:

  • It is a pre-emptive bid, and will hopefully cause even more problems for the opposition than it does for opener's side.
  • It is highly likely that responder will have at least as many cards in the other major as he does in the suit that opener actually holds. If opener has hearts and responder has 3-card heart support then the partnership should probably be playing in at least 3H; provided that responder has at least three spades as well, he will know that it is safe to bid 3H because his support for a spade suit would be just as good.
  • If this is one of the rare deals where responder is actually shorter in the other major, then the opponents will almost always have a fit there and probably ought to be playing in that suit. If they do bid that suit, then this will let responder know what is going on.
  • Because opener has a long major, if the hand belongs to opener's side, the most likely denomination is opener's suit. So responder will not often need to find out much more information than what opener's suit is. If opener's suit was a minor there would be much more information needed, and this would be difficult to get since you are already a step behind by not knowing what opener's suit is immediately.
But the important thing to note is that these points are very specific to the multi-2D bid. If you were to think of a different multi-way bid which did not have homogeneity in its one-bid hand types, you would have to try to find different ways to justify it. In many cases, the bid simply does not work. If you ignore the homogeneity principle you have to be very careful indeed.

9 comments:

Martin Carpenter said...

A more sucessful case for breaking homogenity than the multi comes with either/or two suiters.

These have the additional advantage over the multi of turning weak two bid hands into conditional one bid hands.

I know they've have mostly been used as preempts - but one of the polish forcing pass systems used these at the one level.

I guess these bids show that you can use shape rather than strength to control broken homogeneity with one bid hands.

But you have to have a BIG difference in the shapes - and current system regulations aren't friendly :)

btw some of the earlier posts did seem to somewhat equate the MAFIA (majors first) style of systems like blue team club with canape.

The first has to do with saving space where as the second is just another (quite different) way to show two suiters. No length ambiguities at least.
(at the eccentric extreme of German Moscito even one suiters were opened in a fragment.....).

These are very rare nowadays though - I think perhaps because opening a 4 card minor ahead of a 5+ major on a one bid hand really isn't nice.

Still Roman Club won a few Bermuda Bowls - I've tried to patch transfer openings onto it but I'm not sure how well it works.

Anonymous said...

Martin, what sort of thing do you mean by either/or two-suiters? Polish Twos, RCO Twos, either?

I guess there's actually less ambiguity with RCO Twos, it's more likely that responder can guess the suits from his hand.

Should a hand that passes initially then takes a call be described as a one-bid or a two-bid hand? You can still get preempted, etc, so maybe the terminology should be two-*call* hand - that doesn't sound as good though :(

As for one-level openings, I'd imagine a 1D opening showing 4M5m would do okay - responder's double would be pass-or-correct. Occasionally you'd get a bad score when you double the opponents in a major suit and it turns out that both sides had a big minor suit fit - I guess one-level openings need to be too frequent to allow a big enough difference in shape for this sort of thing not to occur?

And yes, full canapé is a bit weird. I'm struggling to see the advantages.

Mike

Martin Carpenter said...

Yes stuff like RCO two's. Some of the forcing pass system used these at the one level, ie 1H = 45+ H&C/S&D or something.

Full canape is simply different I think. It affects your constructive structure as much anything else, ie Roman in response to 1D has:
1H = Negative - now show side suit and strength, 1NT = Nearly GF balanced, new suits strong too.

In competitive terms it serves to deemphasise the shape in responders hand - any side suits partner has are 5+ long.
So you never need to look for 4-4 fits (the opening bid finds these), and there's no real rush to even show 5 card suits. Also your negative doubles can be very 'loose'.

What hurts of course is the chance to sometimes miss 5-5 fits :)

I do find it fascinating how Roamn club has vanished so competely - it was played by more of the blue team than blue team club and won endless word titles.
I guess much of it got absorbed into Polish club etc but not the canape.

Still with the pedigree it has it's a bit baffling - nothing obviously wrong with it.

Actually David might like it - all the balanced hands open 1C or 1NT (17-20) (maybe 2NT too) and 1D/H/S are forcing for one round, always unablanced and virtually unlimited.
(All GF hands open 1C in traditional style, along with ~16+ C hands. C one suiters are considered not to exist and opened in fake canape suits :)).

Ok the 2C/D 3 suited openings are silly, and 2H/S as 12-15 5+ suit,4+C is slightly annoying.

But 3 suiters can go onto 1C, freeing 2C for some C one suiters etc etc.

I'm sure it would be easy enough to make it extremely playable. The reason for transfer openings btw was to make the unbal openings unlimited and allow for transfer *rebids* by opener.

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