General Information About BBO Robots

General Information about BBO Robots

This section gives general information about BBO robots, under the following headings: 1. Origin and History To Date of Computer Bridge 2. GIB Robots 2.1 GIB System Notes 3. Advanced GIB Robot System Notes

1. Origin and History To Date of Computer Bridge This section is derived from the Wikipedia entry on Computer Bridge, (https://en.wikipedia.org/wiki/Computer_bridge), and may be of interest to all levels of CBC members. Computer bridge is the playing of the game contract bridge using computer software. After years of limited progress, since around the end of the 20th century the field of computer bridge has made major advances. The GIB robot system won the world computer bridge championship in 1997 and 1998 but not since, as other bidding and play systems have emerged. The Wikipedia entry (click here) includes written material and links under the following categories:

• World Computer-Bridge Championship • Computers versus humans • Cardplay algorithms • Comparison to other strategy games • The future

2. GIB Robots This section describes the general characteristics of BBO’s GIB robots, their bidding system and approach to both declarer play and defense.

Most of the material was sourced from the BBO website. The links to specific items referenced in the material (eg. the standard GIB Convention card, and, understanding GIB bid explanations) can be found in the ‘how-to section which follows.‘

Bridge Base Online offers GIB to its users, either for free or at a small cost depending on when and how it is used. GIB is a bridge-playing robot, or computer program. Since GIB is a computer, there are certain things it does really well as a bridge player.

For example, GIB never miscounts a suit. It never misses a spot card. It never forgets its own system. It never fails to notice… well, anything. . Robots play at least as well as the average BBO member. In simulations, GIB robots currently average around 55% in a duplicate tournament setting.

However, GIB is far from perfect. When GIB does make an error, it tends to be a dramatic error of the type that humans would rarely make. Why does this happen? There are quite a lot of reasons. GIB may be programmed incorrectly for the auction. GIB may have misunderstood what someone else meant by their bid, and reached a faulty conclusion. Sometimes when GIB doesn’t know what to do, it examines a bunch of simulated hands to reach a decision, and although those simulations tend to be quite accurate, they can from time to time reach a silly conclusion for a variety of reasons.

The robots are quiet and polite. They may never thank you for a well-played hand, but they will never yell at you for not making a contract. Interaction between the human opponents is not allowed so there is no chance of cross table abuse. Their personal hygiene is impeccable.

The robots used on BBO are called GIB (Ginsberg's Intelligent Bridgeplayer.) GIB is widely considered to be one of the best computer bridge programs ever created. It is occasionally capable of brilliance. It is also occasionally capable of some really poor bids and plays (just like all human players).

Some players may find it frustrating if a particular robot partner plays especially poorly (or if a particular robot opponent plays especially well), on a given hand, but, these things will even themselves over time. Sometimes the robot does something totally crazy (don't we all.) But everyone has the same robot as partner and opponent so everyone is on a level playing field. If your GIB does something crazy, BBO wants to know about it so we can see if it is fixable. (ed. Note: the GIB robots, developed in the late 1990’s are now on version 40, last time I looked, so there have been lots of improvements and debugs)

The GIBs used on BBO play a relatively simple and natural 2/1 bidding system. You can find out the meaning of any bid by clicking on that bid as it appears in the bidding diagram. Furthermore, when it is your turn to bid, moving your mouse over the buttons for the various possible bids will cause an explanation of the bid you are considering (as your GIB partner will understand it), to be displayed. These explanations can be somewhat cryptic, but reading them carefully before you bid will help you to avoid misunderstandings with your GIB partner.

2.1 GIB System Notes

BBO has created a standard convention card for GIB. Click here to see GIB's convention card, and click here for the Basic Robot System Notes, and click here for the Advanced Robot System Notes

In general, the GIB robots on BBO use the 2/1 system described below. You can click on any of GIB's bids for an explanation, and pause your mouse over a bid you plan on making to see how it will understand it. Click here for help understanding these explanations.

3. GIB Advanced System

When you purchase robots on BBO, you have a choice of Basic or Advanced. Advanced is more expensive, and offers a slightly different, more reliable system. Click here to see the Advanced system notes. (the next level of click access material starts here)

2.1 GIB System Notes

Overview

2/1 Game Force with 5 card majors, strong NT, strong (17+) jump shift, weak 2 bids and a strong artificial 2♣.

HCP vs Total Points

Gib uses both old fashioned HCP (A=4, K=3, Q=2, J=1)) and “Total points” (HCP+3 for void, 2 for singleton, 1 for doubleton, but short suits containing an honor are reduced by 1 point). It will usually force to game if it thinks it has 25 Total Points between the two hands.

How GIB Defends

It's difficult to describe precisely how GIB defends. It doesn't use rules and guidelines, like humans often do. It simulates hands based on the auction, using double dummy analysis to determine the average result of each defensive play, and chooses the one with the best average. Sometimes this simulation comes up with the same choice that a human would make (there's a good reason for some of the guidelines -- they actually work well), but not always (some of our rules of thumb have become popular simply because they're easy to remember and "good enough"). When it has a choice of equivalent cards, it will choose based on leading and signalling conventions.

GIB doesn't interpret your signals or make many inferences from the play, it uses simulations based on the auction. However, it's usually able to figure out that when you lead an honor, it's part of a sequence.

GIB usually leads passively against NT (read the book Winning Notrump Leads to understand why). Don't assume it's leading its longest suit. When you lead, it doesn't assume you're leading your best suit, which is why it doesn't always return the suit like a human would.

In suit contracts, GIB's opening lead is frequently a side singleton or doubleton, to try to get a ruff. When it leads a suit bid by the opponents, this is almost always the reason. Read the book Winning Suit Contract Leads for insight on the way GIB leads against suits.

If it leads an honor that's part of a sequence, it uses standard honor leads (K from AKx, A from AK doubleton). If it leads from a long suit, it leads 4th best (but see above: it doesn't always lead its long suit). When leading from 3 small, it leads low against both suit and NT contracts.

It doesn't use any signals when making discards, it just tries to make safe discards. In a suit contract it will frequently discard from a short suit while it has trumps left. Otherwise, it tends to discard from a long suit that's safe to shorten.

When it's following to partner's opening lead, it will usually give an attitude signal:

• High spot card with an Ace or King • High spot card with a Queen behind dummy's Ace or King • Low in any other situation

Note that it doesn't give count in this situation, so it's hard to know when you can give it a ruff.

When it's trying to win the trick in third hand, it will play the lowest of equals. Otherwise, when following suit it usually gives standard count signals (high = even); an exception is when it's forced to play equivalent cards in a doubleton, it will randomize them because of "restricted choice".

(end of intro)

GIB Basic Robot System Notes

Bidding

Basic Approach

Opening bids

1♣ could be 3 if 4333,3433 or 4423. 2♣ response is forcing, inverted usually 4 unless 4432. Opens 1♦ with 4-4 in the minors. 2♦ response is forcing, 1♦ inverted. 2♣ response is game forcing. normally show 5 in all seats. Opens 1♠ with 5-5 in spades and clubs. 1M-2M 1♥ 1♠ direct raise shows 7-10 points. 1N response is forcing. Jacoby 2NT. Splinters. Two-way game tries. balanced 15-17 HCP, may have a 5-card major (GIB treats 17 with 5-card major 1NT as 18). Followups 2♣ strong, artificial. 22+ HCP 2♦ 2♥ 2♠ weak 2 bid. Disciplined, with honors in the suit 2NT balanced 20-21 HCP, may have a 5-card major. Followups

Responses and Rebids

• Opening jump rebid (1♣-1any-3♣ for example) promises 6+ card, 17-20 HCP • Opening major rebid after 2/1 response does not promise 6 cards in the suit. • Jacoby 2NT • Raising responder's suit usually promises 4 cards, but will occasionally raise with only 3

Competitive Auctions

• 1-level overcall shows 5+; 8-17 HCP; 9-19 TP. However, might overcall 1-major with decent hand and a strong 4-card suit. • GIB uses the law of total tricks. • Takeout doubles to 4♥ • Negative X and Responsive X up to 3♠, Support X up to 2♥ (GIB may do support X with Kx). • Weak jump overcalls (aggressive, 3-9 HCP, no allowance for vulnerability) • Cappelletti when opponents open 1NT (aka Hamilton) • Lebensohl after 1NT, double of weak 2, and after reverse. • Michaels cue bid (over a weak 2 in a major, 4 of the same major shows a good hand with both minors, while 4NT shows a weaker hand with both minors). • Unusual NT (when non-vulnerable GIB only does Unusual NT with intermediate hands, xx-KQxxxx KQxxx for example, but it needs a better hand when vulnerable) • Unusual versus Unusual, lower cue = limit raise or better (GIB does UVU, but doesn't alert it with this name) • Sandwich 1NT (by passed hand only) • Truscott after partner's opening doubled (aka Jordan)

Other conventions and treatments

• Fourth Suit Forcing (1♣-1♦-1♥-1♠ is artificial game force, 1♣-1♦-1♥-2♠ is game forcing with spades) • New minor forcing (one-way) • Roman Key Card Blackwood. GIB doesn't like to use Gerber, but it will respond appropriately • Strong (Soloway) jump shifts by unpassed hand, fit jumps by passed hand (except jumps to 3♣, which are natural and invitational). • Reverse Drury by passed hand in uncontested auctions.

Notes

• Vulnerability does not affect most opening/overcall decisions. GIB tends to consider vulnerability and form of scoring only when thinking about leaving in a double for penalties, and other high-level competitive decisions (they get used when performing simulations and estimating the expected value of different outcomes). Some bidding rules, such as the decision whether to use Michaels or Unusual NT, take vulnerability explicitly into account; these were decided on a case-by-case basis, there's no general rule.

Conventions that GIB does not play

• Gambling 3NT • Namyats • Bergen or Reverse Bergen Raises • DONT • Puppet Stayman

Two-way Game Tries

After a single raise of a major suit, GIB plays two-way game tries.

• The next step (1♥-2♥-2♠, 1♠-2♠-2NT) is a short-suit game try, showing unspecified shortness. Responder can bid the next step above that (2NT or 3♣) to ask where the shortness is. Opener bids the short suit, or bids his major if the short suit is one of the step suits. • Any other bid below 3 of the major is a long suit game try, at least a 3-card suit with some honors. After 1♥-2♥, 2NT is a LSGT in spades (since 2♠ would be a short-suit game try). • 3 of the major is a general strength game try, showing about 17 points with no singleton or void (GIB rarely makes this bid, since this would probably be a 1NT opener).

Roman Keycard Blackwood (RKCB)

RKCB is a 4NT bid that, unlike regular Blackwood, asks for "keycards" instead of Aces. There are always 5 keycards - the 4 Aces plus the King of the agreed trump suit. If no trump suit has been clearly agreed, the King of the most recently bid suit is typically counted as the 5th keycard. Responses to 4NT RKCB 0314: • 5♣ 0 or 3 keycards • 5♦ 1 or 4 keycards • 5♥ 2 or 5 keycards, but no Queen of the agreed suit • 5♠ 2 or 5 keycards plus Queen of the agreed suit • 5NT An even number of keycards plus an unspecified void • 6x An odd number of keycards with a void. If 6x is below 6 of the agreed suit then the void is in the suit bid. If 6x is a bid in the agreed suit then the void is in an unspecified higher-ranking suit.

After the 5♣ and 5♦ responses, the 4NT bidder can bid the next step that is not a signoff in order to ask for the Queen of the agreed suit. Then: • Bidding the agreed suit at the cheapest level denies the Queen of the agreed suit. • Bidding a new suit promises the Queen of the agreed suit plus the King of the suit bid. • Bidding 5NT promises the Queen of the agreed suit and denies a side King that can be shown below 6 of the agreed suit.

A subsequent 5NT bid by the 4NT bidder (regardless of whether or not an ask for the Queen of the agreed suit has taken place) asks for specific Kings. The 5NT bid promises that all of the 5 keycards and the Queen of the agreed suit are accounted for. Then: • The responder to RKCB is entitled to bid a grand slam if he thinks that 13 tricks rate to be available. • If the responder to RKCB has a King that is lower-ranking than the agreed suit, he should bid that suit at the 6-level. If he has more than one such King, he should bid his lowest- ranking King. • Otherwise the responder to RKCB should bid 6 of the agreed suit.

DOPI after interferences: • Interference after 4NT (whether RKCB or regular Blackwood) is handled by the DOPI convention. • Double with 0 keycards (or ace, playing regular blackwood), pass with 1 keycard (or ace, playing regular blackwood).

After a 1N opening bid

If the opponents overcall 2♣ (Cappelletti any 1-suited hand), Double is Stayman and all other bids as below. If the opponents double, all systems are on; Redouble is used to run out to a minor (opener should bid 2♣, responder passes or corrects to 2♦). After any other interference, Lebensohl is used.

• 2♣ Stayman (promises at least one 4-card major unless inviting 3NT). o 2♦ No 4-card major ▪ 2♥/2♠ Invitational with 5 of the suit bid and 4 of the other major ▪ 2NT Invitational (does not promise a 4-card major) ▪ 3♣/3♦ 5+ card suit. Forcing to game ▪ 3♥/3♠ Smolen (forcing to game with 4 of the suit bid and 5 of the other major) ▪ 4NT Invitational to 6NT. o 2♥ 4 hearts (could also have 4 spades) ▪ 2♠ Invitational with 4 spades ▪ 2NT Invitational, denying 4 spades ▪ 3♣/3♦ 5+ card suit. Forcing to game ▪ 3♥ Invitational ▪ 3♠ Artificial slam try with at 4+ hearts, usually balanced ▪ 4♣/4♦ Splinters (singleton or void in the suit bid, 4+ hearts, interest in slam) ▪ 4NT Invitational to 6NT o 2♠ 4 spades (denies 4 hearts) ▪ 2NT Invitational (does not promise 4 hearts) ▪ 3♣/3♦ 5+ card suit. Forcing to game ▪ 3♥ Artificial slam try with 4+ spades, usually balanced. ▪ 3♠ Invitational ▪ 4♣/4♦/4♥ Splinters (singleton or void in the suit bid, 4+ spades, interest in slam) ▪ 4NT Invitational to 6NT • 2♦ Jacoby Transfer Bid (promises 5+ hearts). Opener would normally bid 2♥, but can superaccept with a maximum and 4-card heart support. After 2♥: o 2♠ 5+ hearts, 5+ spades, invitational to game. o 2NT Exactly 5 hearts, invitational to game. o 3♣/3♦ 5+ hearts, 4+ card suit. Forcing to game. o 3♥ Invitational with 6+ hearts o 3NT Exactly 5 hearts. Choice of games (4♥ or 3NT). o 3♠/4♣/4♦ Splinters (6+ hearts, singleton or void in the suit bid, interest in slam) o 4♥ 6+ hearts, no singleton or void, mild slam interest o 4NT Exactly 5 hearts. Invitational to 6♥ or 6NT o 5NT Choice of slams (6♥ or 6NT) • 2♥ Jacoby Transfer Bid (promises 5+ spades). Opener would normally bid 2♠, but can superaccept with a maximum and 4-card spade support. After 2♠: o 2NT Exactly 5 spades, invitational to game. o 3♣/3♦ 5+ spades, 4+ card suit. Forcing to game. o 3♥ 5+ spades, 5+ hearts. Forcing to game. o 3♠ Invitational with 6+ spades o 3NT Exactly 5 spades. Choice of games (4♠ or 3NT). o 4♣/4♦/4♥ Splinters (6+ spades, singleton or void in the suit bid, interest in slam) o 4♠ 6+ spades, no singleton or void, mild slam interest o 4NT Exactly 5 spades. Invitational to 6♠ or 6NT o 5NT Choice of slams (6♠ or 6NT). • 2♠ Minor Suit Stayman (Usually at least 54 in the minors, forcing to game) o Opener would normally bid a 4+ card minor if he had one, but can bid 2NT with 3343 or 3334 distribution. o If responder's next bid is 3 of a major, he is promising a singleton or void in that suit, but not necessarily slam interest • 2NT Minor Suit Transfer (Promises 6+ clubs. Opener must bid 3♣) o If responder's next bid is 3 of a new suit, he is promising a singleton or void in that suit, but not necessarily slam interest o Responder's 3NT rebid is a mild slam try (usually balanced). o Responder's 4NT rebid is RKCB • 3♣ Minor Suit Transfer (Promises 6+ diamonds. Opener must bid 3♦) o If responder's next bid is 3 of a new suit, he is promising a singleton or void in that suit, but not necessarily slam interest o Responder's 3NT rebid is a mild slam try (usually balanced). o Responder's 4NT rebid is RKCB • 3♦/3♥/3♠ Singleton or void in the suit bid, at least 4 cards in the other 3 suits, no 5card major, forcing to game. • 3NT Signoff • 4♣ Gerber • 4♦ Texas Transfer (Promises 6+ hearts, opener must bid 4♥) o New suit rebid by responder is a cuebid. o 4NT rebid by responder is RKCB. • 4♥ Texas Transfer (Promises 6+ spades, opener must bid 4♠) o New suit rebid by responder is a cuebid. o 4NT rebid by responder is RKCB. • 4NT Invitational to 6NT • 5NT Invitational to 7NT

After a 2N opening bid

• 3♣ Stayman (promises at least one 4-card major) o 3♦ No 4-card major ▪ 3♥/3♠ Smolen (forcing to game with 4 of the suit bid and 5 of the other major) ▪ 4♣/4♦ 5+ card suit. Interest in slam ▪ 4♥/4♠ Signoff bids ▪ 4NT Invitational to 6NT o 3♥ 4 hearts (could also have 4 spades) ▪ 3♠ Artificial slam try with 4+ hearts ▪ 3NT Choice of games (4♠ or 3NT). Promises 4 spades. ▪ 4♣/4♦ 5+ card suit. Interest in slam ▪ 4NT Invitational to 6NT o 3♠ 4 spades (denies 4 hearts) ▪ 3NT Signoff (promises 4 hearts) ▪ 4♣/4♦ 5+ card suit. Interest in slam. ▪ 4♥ Artificial slam try with 4+ spades ▪ 4NT Invitational to 6NT • 3♦ Jacoby Transfer Bid (promises 5+ hearts). Opener would normally bid 3♥, but can superaccept with a maximum and 4-card heart support. After 3♥: o 3♠ 5+ hearts, 5+ spades, interest in slam o 3NT Exactly 5 hearts. Choice of games (4♥ or 3NT) o 4♣/4♦ 5+ hearts, 4+ cards in suit bid, forcing to game o 4♥ Mild slam try with 6+ hearts o 4NT Exactly 5 hearts. Invitational to 6♥ or 6NT o 5NT Choice of slams (6♥ or 6NT) • 3♥ Jacoby Transfer Bid (promises 5+ spades). Opener would normally bid 3♠, but can superaccept with a maximum and 4-card spade support. After 3♠: o 3NT Exactly 5 spades. Choice of games (4♠ or 3NT) o 4♣/4♦ 5+ spades, 4+ cards in suit bid, forcing to game o 4♥ 5+ spades, 5+ hearts, choice of games (4♥ or 4♠) o 4♠ Mild slam try with 6+ spades o 4NT Exactly 5 spades. Invitational to 6♠ or 6NT o 5NT Choice of slams (6♠ or 6NT) • 3♠ Minor Suit Stayman (usually at least 54 in the minors, forcing to game) o Opener would normally bid a 4+ card minor if he had one. Otherwise he would bid 3NT. o If responder's next bid is 4 of a major, he is promising a singleton or void in that suit • 3NT Signoff • 4♣ Gerber • 4♦ Texas Transfer (Promises 6+ hearts, opener must bid 4♥) o New suit rebid by responder is a cuebid. o 4NT rebid by responder is RKCB. • 4♥ Texas Transfer (Promises 6+ spades, opener must bid 4♠) o New suit rebid by responder is a cuebid. o 4NT rebid by responder is RKCB. • 4NT Invitational to 6NT • 5NT Invitational to 7NT

Soloway Jump Shifts

GIB plays Soloway Strong Jump Shifts by an unpassed hand in uncontested auctions. A jump shift shows one of the following types of hands: 1. Strong rebiddable suit, 17+ total points, 4+ controls (A=2, K=1), no side 4-card suit 2. Solid suit, 17+ total points, 4+ controls, may have a side 4-card suit 3. Rebiddable suit, 18+ HCP, 4+ controls, 5332 or 6322 shape. 4. Rebiddable suit, 17+ total points, 4+ controls, 4-card support for opener's suit

Strong jump shifts are only from the 1 level to a higher suit on the 2 level. Jumps to a lower suit on the 3 level are natural and invitational.

Opener can rebid his suit to show 6+, raise responder or bid RKC Blackwood with 3+ support, bid a side suit to deny support and show least KQ in the suit, or bid NT at the cheapest level to show any other hand.

Jump shifter shows which type of hand it had with its next bid: • With types 1 or 2, it rebids its suit, jumping to game with a minimum and solid suit (note that it never shows the side suit in type 2). • With type 3, it bids NT or raises NT to game. • With type 4, it raises opener's suit with no side shortness, or bids its short suit (this is why it can never show its own side suit – a new suit is a splinter in support of opener).

Reverse Drury

GIB plays one-way Reverse Drury when partner opens a Major in 3rd or 4th seat. A 2♣ response shows at least 3-card support and invitational values (11-12 total points). This is not used if there is any interference; Jordan/Truscott 2NT is still used to show a limit raise over a double, a cue bid is used after an overcall, and 2♣ is natural (weak after a double, one-round force after an overcall).

Opener's rebids are as follows: • 2♦ Full opener, inviting game, no extra shape. • 2M Sub-minimum opener, no interest in game. • New suit without jumping 4+ cards in the suit, less than 18 total points. • New suit single jump 18+ total points, singleton in suit bid. • New suit double jump 18+ total points, void in suit bid. • 2NT 5332 shape, one-round force, less than 18 total points. • 3NT 6322 shape, one-round force, less than 18 total points. • 3M 18+ total points, balanced. • 4M To play, nothing extra to show.

(end of Basic system section)

(beginning of Advanced GIB Robot System Notes

BBO Advanced (2/1=Game Force)

Notrump Openings

1NT=15-17: Stayman, Jacoby, 2♠->3♣, 2♠->3♣, 2NT- >3♦, 3♣=5-5 minors weak, 3♦=5-5 minors GF, 3♥=31(54), 3♠=13(54), Gerber, Texas 2NT=20-21: Stayman, Jacoby, Texas, Gerber, 3♠->3NT (minor 1 or 2-suiter) 3NT=Solid minor no outside A/K

Major Suit Openings Minor Suit Openings

1♥/♠=5+: 1NT=forcing, Jacoby 1♣/♦=3+, 2NT=11-12; 2NT, 3NT=15-17, Splinters, 3NT=13-15, 1♣-1NT=8- Weak jump raises, 3♣=limit 10, Inverted raises, 1♦- raise (4+), 3♦=good raise (4+), 3♣=invitational 1♠-3♥=weak

2-Level Openings 2♣=strong: 2♦=waiting, 2♥=negative, 2NT=♥ positive 2♦/♥/♠=weak: 2NT=asks feature; new suits forcing

Other important notes 4th suit game force, Unusual vs. Unusual, Ingberman over reverses (2NT=negative), 2-way NMF, Wolff over 2NT rebids

Doubles Notrump Overcalls Negative->4♦, Responsive->4♦, 1NT=15-18 (system on) 2NT=unusual (2 lowest unbid) Support x and xx ->2-level, Maximal

Simple Overcalls Over 1NT Openings

8-16+ HCP; new suit=non-forcing; DBL=penalty 1NT=strong (Cappelletti): 2♣=any suit, jump raise=weak; cuebid=limit 2♦=majors, 2♥=♥+minor, 2♠=♠+minor 1NT=weak (Landy): raise+ 2♣=majors, 2♦/♥/♠=natural

Jump Overcalls Over Takeout Doubles

New suit forcing at 1-level; RDBL=10+ HCP; 2NT=limit raise+; Weak jump raise=weak; jump shift=weak;

Direct Cuebid Slam Bidding

Michaels RKCB 1430; Gerber; Grand slam force; DOPI; DEPO

Defensive Carding

Attitude: high=encouraging; low=discouraging Count: high-low=even; low-high=odd; 4th best leads; Ace from AKx versus suits

(start of Wikipedia article on computer bridge)

Computer bridge From Wikipedia, the free encyclopedia Computer bridge is the playing of the game contract bridge using computer software. After years of limited progress, since around the end of the 20th century the field of computer bridge has made major advances. In 1996 the American Contract Bridge League (ACBL) established an official World Computer-Bridge Championship, to be held annually along with a major bridge event. The first championship took place in 1997 at the North American Bridge Championships in Albuquerque. Since 1999 the event has been conducted as a joint activity of the American Contract Bridge League and the World Bridge Federation. Alvin Levy, ACBL Board member, initiated this championship and has coordinated the event annually since its inception. The event history, articles and publications, analysis, and playing records can be found at the official ebsite.

Contents

• World Computer-Bridge Championship • Computers versus humans • Cardplay algorithms • Comparison to other strategy games • The future • See also • References • External links

World Computer-Bridge Championship The World Computer-Bridge Championship is typically played as a round robin followed by a knock-out between the top four contestants.[1][2] Winners of the annual event are:

• 1997 Bridge Baron • 1998 GIB • 1999 GIB • 2000 Meadowlark Bridge • 2001 Jack • 2002 Jack • 2003 Jack • 2004 Jack • 2005 Wbridge5 • 2006 Jack • 2007 Wbridge5 • 2008 Wbridge5 • 2009 Jack • 2010 Jack • 2011 Shark Bridge • 2012 Jack • 2013 Jack • 2014 Shark Bridge • 2015 Jack • 2016 Wbridge5[3] • 2017 Wbridge5[4] • 2018 Wbridge5[5] • 2019 Micro Bridge[6] • 2020 championship has been cancelled

Computers versus humans In Zia Mahmood's book, Bridge, My Way (1992), Zia offered a £1 million bet that no four-person team of his choosing would be beaten by a computer. A few years later the bridge program GIB (which can stand for either "Ginsberg’s Intelligent Bridgeplayer" or "Goren In a Box"),[7] brainchild of American computer scientist Matthew Ginsberg,[8] proved capable of expert declarer plays like winkle squeezes in play tests. In 1996, Zia withdrew his bet. Two years later, GIB became the world champion in computer bridge, and also had a 12th place score (11210) in declarer play compared to 34 of the top humans in the 1998 Par Contest (including Zia Mahmood).[9] However, such a par contest measures technical bridge analysis skills only[clarification needed], and in 1999 Zia beat various computer programs, including GIB, in an individual round robin match.[10] Further progress in the field of computer bridge has resulted in stronger bridge playing programs, including Jack [11] and Wbridge5.[12] These programs have been ranked highly in national bridge rankings. A series of articles published in 2005 and 2006 in the Dutch bridge magazine IMP describes matches between five-time computer bridge world champion Jack and seven top Dutch pairs including a Bermuda Bowl winner and two reigning European champions. A total of 196 boards were played. Jack defeated three out of the seven pairs (including the European champions). Overall, the program lost by a small margin (359 versus 385 IMPs).[volume & issue needed] In 2009, Phillip Martin, an expert player, began a four-year project in which he played against the champion bridge program, Jack. He played one hand at one table, with Jack playing the other three; at another table, Jack played the same cards at all four seats, producing a comparison result. He posted his results and analysis in a blog he titled The Gargoyle Chronicles.[13] The program was no match for Martin, who won every contest by large margins.

Cardplay algorithms Bridge poses challenges to its players that are different from board games such as chess and go. Most notably, bridge is a stochastic game of incomplete information. At the start of a deal, the information available to each player is limited to just his/her own cards. During the bidding and the subsequent play, more information becomes available via the bidding of the other three players at the table, the cards of the partner of the declarer (the dummy) being put open on the table, and the cards played at each trick. However, it is only at the end of the play that full information is obtained. Today's top-level bridge programs deal with this probabilistic nature by generating many samples representing the unknown hands. Each sample is generated at random, but constrained to be compatible with all information available so far from the bidding and the play. Next, the result of different lines of play are tested against optimal defense for each sample. This testing is done using a so-called "double-dummy solver" that uses extensive search algorithms to determine the optimum line of play for both parties. The line of play that generates the best score averaged over all samples is selected as the optimal play. Efficient double-dummy solvers are key to successful bridge-playing programs. Also, as the amount of computation increases with sample size, techniques such as importance sampling are used to generate sets of samples that are of minimum size but still representative.

Comparison to other strategy games[edit] While bridge is a game of incomplete information, a double-dummy solver analyses a simplified version of the game where there is perfect information; the bidding is ignored, the contract (trump suit and declarer) is given, and all players are assumed to know all cards from the very start. The solver can therefore use many of the game tree search techniques typically used in solving two-player perfect-information win/lose/draw games such as chess, go and reversi. However, there are some significant differences.

• Although double-dummy bridge is in Unsolved problem in practice a competition between two generalised computer science: players, each "player" controls two hands and the cards must be played in a correct order that Is the problem of deciding the reflects four players. (It makes a difference which winner in double-dummy of the four hands wins a trick and must lead the bridge hard in any complexity next trick.) class? • Double-dummy bridge is not simply (more unsolved problems in win/lose/draw and not exactly zero-sum, but computer science) constant-sum since two playing sides compete for 13 tricks. It is trivial to transform a constant-sum game into a zero-sum game. Moreover, the goal (and the risk management strategy) in general contract bridge depends not only on the contract but also on the form of tournament. However, since the double-dummy version is deterministic, the goal is simple: one can without loss of generality aim to maximize the number of tricks taken. • Bridge is incrementally scored; each played trick contributes irreversibly to the final "score" in terms of tricks won or lost. This is in contrast to games where the final outcome is more or less open until the game ends. In bridge, the already determined tricks provide natural lower and upper bounds for alpha-beta pruning, and the interval shrinks naturally as the search goes deeper. Other games typically need an artificial evaluation function to enable alpha-beta pruning at limited depth, or must search to a leaf node before pruning is possible. • It is relatively inexpensive to compute "sure winners" in various positions in a double- dummy solver. This information improves the pruning. It can be regarded as a kind of evaluation function, however while the latter in other games is an approximation of the value of the position, the former is a definitive lower bound on the value of the position. • During the course of double-dummy game tree search, one can establish equivalence classes consisting of cards with apparently equal value in a particular position. Only one card from each equivalence class needs to be considered in the subtree search, and furthermore, when using a transposition table, equivalence classes can be exploited to improve the hit rate. This has been described as partition search by Matthew Ginsberg. • Numerous strategy games have been proven hard in a complexity class, meaning that any problem in that complexity class can be reduced in polynomial time to that problem. For example, generalized x × x chess has been proven EXPSPACE-complete (both in EXPSPACE and EXPSPACE-hard), effectively meaning that it is among the hardest problems in EXPSPACE. However, since there is no natural structure to exploit in double- dummy bridge towards a hardness proof or disproof, unlike in a board game, the question of hardness remains.[14]

The Future

In comparison to computer chess, computer bridge has not reached world-class level, but the top robots have demonstrated a consistently high level of play. (See analysis of the last few years of play at www.computerbridge.com.) However see below the Philippe Pionchon's article (1984). Yet, whereas computer chess has taught programmers little about building machines that offer human-like intelligence, more intuitive and probabilistic games such as bridge might provide a better testing ground. The question of whether bridge-playing programs will reach world-class level in the foreseeable future is not easy to answer. Computer bridge has not attracted an amount of interest anywhere near to that of computer chess. On the other hand, much progress has been made in the last decade by researchers working in the field. Regardless of bridge robots' level of play, computer bridge already has changed the analysis of the game. Commercially available double-dummy programs can solve bridge problems in which all four hands are known, typically within a fraction of a second. These days, few editors of books and magazines will solely rely on humans to analyse bridge problems before publications. Also, more and more bridge players and coaches utilize computer analysis in the post-mortem of a match.