[thepossum]

Hi

Apologies if these are covered in historic threads. I have tried searching and can't find anything very recent on the matter

It relates to some of the core assumptions, terminology and discussions about DD. Excuse me if my questions seem naive

1. Best Declarer vs Best Defence

To me that suggests if you had two top Bridge pairs playing each other, how they would play the hand - sorry it's like two expert declarers
Double Dummy on the other hand treats Best as knowing more about the layout than even an expert would deduce

2. Adjusting play for safety

Do many DD solvers make adjustments for safety when necessary
A simplistic statistical analysis would make errors - do the best ones always place making a contract ahead of "best" average score
Maybe (some) top players always go for best average

Hope those questions make sense. I have other similar ones but they are two that keep cropping up when I look at the solutions DD analysis provides

[steve2005]

DD declarer tries to maximize the number of tricks, knowing the layout of the hands.
It doesn't play safe as it knows if the finesse will fail.
The double dummy examines all possible plays and determines the best play given that the defender will also make the best play at it's turn.

[thepossum]

steve2005, on 2025-January-13, 21:42, said:

DD declarer tries to maximize the number of tricks, knowing the layout of the hands.
It doesn't play safe as it knows if the finesse will fail.
The double dummy examines all possible plays and determines the best play given that the defender will also make the best play at it's turn.

I know all that. I am asking more philosophical questions about what best declarer and best defence is

That is what I prefer to compare myself against

I believe some have even analysed slams and asked questions why professionals and other top players don't make (or even bid) many DD slams

Would it not be a cool mode to switch on and off. Professional or expert mode

[mycroft]

I know this has changed somewhat in the last 10 years, but (from a side direction) here's the issue:

Why are robots bad? Because they use double dummy simulations to "simulate" single dummy analysis.

Why do robots do this? Because single dummy analysis is an unsolved problem (or, at least, SDAnalyzers are currently worse than simulate from multiple DD analyses.

Given that, the answer to your question is "without paying an expert to analyze every hand SD, from both directions, there is no way to give you this answer."

We would all like to have "actual best bridge" analysis on our hands - especially those of us who are directors (or teachers) who have to explain (again) "we beat par by a lot! Why did we score 30%?" And yeah, I had one Sunday night, where "okay, 3NT goes down. But it requires the opening leader to *underlead* ♥AKQxxx at trick 1, so that partner still has a heart to lead when he gets in. I'll applaud the expert who finds that play."

TL, DR; you get DD because what you (and all of us) want Does Not Exist.

Take heart, though; it's also why chess cheaters get caught by "making multiple Stockfish best moves" after (sometimes deliberately, sometimes just their actual skill) playing to get behind in the game; and GIB playing with GIB in an average club game gets 54% for third or fourth.

[mikeh]

As stated earlier in this thread, DD analysis is based on examining all 52 cards….the layout of which is known with 100% accuracy.

Say one is playing in 4S and the key is the location of the spade king…dummy has AQ9x, we hold J10xxx, and we know that RHO has length in both minors and presumably short spades. With no other clue from the bidding or play, all good players will finesse against the king. But DD play always drops the king when it’s singleton offside and always finesses when it’s onside. No non-cheating good player would ever drop the king when it’s stiff offside (unless desperate for a swing and willing to look silly while doing so).

Do NOT ever confuse DD play with ‘expert’ or ‘professional’ play.not only do no players…(other than self-kibitzing cheaters) play double dummy but no good player would ever even try.

There are hands on which a skilled declarer has a very good idea about the opposing hands….I’ve held a few where I was morally certain of how the cards lay as early as trick one or two….but even then I’d not usually be certain about where, say, a missing jack might be. Such hands will occasionally arise when the opps have provided high card and distributional information during the bidding and then further inform from the opening lead and the play by third hand. In those situations it is possible to adopt a line that, to an observer naive to how much information declarer has been given, will appear to be a double dummy line. So there are times when, due to skill and the willingness to draw inferences, the play is basically DD

The key lies in how an expert player deduces the layout and then adopts a line of play. Computers don’t draw inferences. Some day AI may be able to do that but for now they analyze based on being given the data about exactly where every card lies. They don’t ‘care’ whether RHO showed, say, 12 cards in the minors….if the non minor card is the king behind dummy’s AQJx, they drop the king, not because they drew an inference ir played for a very low percentage swing but because they ‘know’ the king is offside.

I used to give lessons at a local club, using the previous week’s hand records. The GIB DD analysis made the effort largely wasted. The players who attended were often fixated on the DD analysis. ‘It says we can make 4S, but we didn’t bid it. What did we do wrong?’

My answer: Spades broke 3-1 with the king singleton offside. Hearts were 4-2, you had Kxx in dummy and AJxx in hand, you can find out (by playing other suits) that LHO has two and RHO had 4….You had to drop the doubleton Queen. So to make, you have to play very badly.

[pescetom]

I agree completely except for:

mikeh, on 2025-January-14, 12:40, said:

The key lies in how an expert player deduces the layout and then adopts a line of play.
Computers don’t draw inferences.
Some day AI may be able to do that

My view here is that current state of the art AI is quite capable of drawing inferences but has not been effectively applied to the problem of playing Bridge, unlike the problems of playing Chess or Go.
Probably because there is too little public interest and economic return, rather than intrinsic difficulty of playing bridge or the complication that is a pairs game with disclosure of agreements (current robots wouldn't even beat the humans at Whist).

[thepossum]

What I am looking for is an analytical approach that essentially plays as two experts against each other not knowing the layout - each can see partner's hand - as DD suggests to me

Which of course makes no sense since they can see the other dummy etc

Let's wait for AI to catch up

All abit sad. Asking a question like this and going round in circles

So AI trained on known experts. Plug in different favourites or styles of play

Why do we play robots using such flawed analysis

[mikeh]

thepossum, on 2025-January-14, 17:53, said:

What I am looking for is an analytical approach that essentially plays as two experts against each other not knowing the layout - each can see partner's hand - as DD suggests to me

Which of course makes no sense since they can see the other dummy etc

Let's wait for AI to catch up

All abit sad. Asking a question like this and going round in circles

So AI trained on known experts. Plug in different favourites or styles of play

Why do we play robots using such flawed analysis

You continue to misunderstand what DD means. It is the very opposite of how expert players approach a hand, although (as I mentioned) there are hands where a DD line is apparent to an expert early on….and many, many hands can be played as if DD by the late stages, because experts are experts precisely because they can figure out where the missing cards are, using a multitude of factors.

Here’s what is almost surely an incomplete list…it reflects what I’m thinking about during the play

1. The bidding, including passes. Their system and their style (often related but not at all the same thing)

2. Against even not top level experts and definitely against non experts, tempo in the bidding and the play. Never partner’s tempo…if it told us something, we lean over backwards to ignore it

3. (As declarer). The opening lead. Not only what card was led, and and what was played by RHO but, often more importantly, what was not led. Most experienced players make fairly ‘normal’ leads. Say your missing KQJ in a suit nobody bid. If LHO doesn’t lead that suit, he almost always lacks KQJ…he may have KJ or Kxx etc but won’t have KQJ and on some hands and leads can be inferred likely not to have KQ or QJ, etc.

4. Given the relative (compared to, say, mid-hand) lack of information, what’s my goal? Am I planning to maximize my chances of making (imp reasoning) or should I be prepared to risk making in order to get a good matchpoint score? Say I’m in 3N with 9 clear winners but I can see that we screwed up or misguessed in the auction and I judge that the ‘field’ will almost all be in the cold mp major suit game. At imps, I don’t much care and won’t ever jeopardize the contract trying to get 630 to best the 620s. At mps, I’ll strain to find a line to make 10 tricks even if it means I may go down in game. Or have I sacrificed? What’s my goal then? If I’m doomed, but it looks as if they might have gone down….in which case going down even one is bad..then I have to try to place the cards such that they make…and play accordingly even if doing so risks extra undertricks

5. As the play goes along, each card played and sometimes cards not played provide further information from which to draw conclusions or inferences.if a suit is 6=2, how does that affect my view of how the other suits lie? Would the bidding have been different on some of those possible lies, and so on. On many hands one at some point knows exact shapes, on others one has only tentative inferences. Again, the use we make of inferences depends on factors such as in number 4 above. Firm conclusions, otoh, narrow options, but also make decisions easier. It’s critical, to becoming a good player, to notice and keep in mind every single card played by the opponents. You also have t try to put yourself in their places. What are their goals? What do they know or infer using all of the same methods declarer uses?


One of my all time favourite hands was against Eddie Wold and Mike Passell. I needed to guess whether a side suit was 3=3 or 4=2. They each played high-low, using udca…so each signalled, completely in tempo, an odd number of cards. Against weak players I’d trust them. But I knew that they knew what my problem was…so I actually felt a little insulted as I played for 4-2, as it was. My other favourite was on defence. I signalled I held a high spade and tyat I didn’t have anything in hearts. My partner smoothly did the opposite. Declarer, an expert, declined the winning heart finesse through me and the winning spade finesse through partner….cashing winners and throwing me in to lead away from my marked spade king. I cashed out…I didn’t have any spades left. I think these two hands would be extremely difficult to reduce to any set of algorithms. On my declarer hand, I had to infer what two WC (far better than I) players would ‘know’ and what they’d see as the best way to fool me.on the defence hand, we both had to collaborate to tell declarer that the hand lay a certain way, relying on his skill to see a way to ‘overcome’ the problem through a strip and endplay. Neither hands could have ‘worked’ against non-experts….on the first, few players falsecard and few would have worked out why it might be advisable. On the second, the average player would have shrugged and taken the finesses not matter what signals we gave…they wouldn’t have seen the endplay possibility


And the defence hand wouldn’t work with an average partner, who wouldn’t encourage in his weak suit or discourage in his strong.

The above is just a list, with no attempt to list them in any kind of order. And it’s not only probably missing points, but it’s definitely compressed. My point isn’t to boast about my skill….there are many players better than I am. But look at the list and compare my approach to how anyone would ‘think’ if, before making any play, they knew where every card was.

I occasionally enjoy a DD problem, but on the whole I find them boring, and of very little relevance to the game of bridge.

[mike777]

[quote name='thepossum' timestamp='1736829176' post='1072467']
I know all that. I am asking more philosophical questions about what best declarer and best defence is

I would suggest a starting point in your quest might be
1. Define best declarer and best defense.
2. Define your standard of measurement

Or are just asking for people's opinions?

[mycroft]

To reduce the insult, a) note they thought that you were good enough to actually notice, and b) very likely *they* had the suit mapped out too, and so when one gave the "wrong" count, the other one noticed and "agreed" in tempo. Because c) they knew that if one gave wrong and the other right, you'd notice (of course) and probably guess which hand was more likely to have lied.