Contract bridge

Contract bridge, or simply bridge, is a trick-taking card game using a standard 52-card deck. In its basic format, it is played by four players in two competing partnerships, with partners sitting opposite each other around a table. Contract bridge involves many skills, including discriminating, blaming your partner, and cheating.
==Gameplay==
===Setup and dealing===
The four players sit in two partnerships, with each player sitting opposite his partner. A cardinal direction is assigned to each seat, so that one partnership sits in North and South, while the other sits in West and East. The cards may be freshly dealt or, in duplicate bridge games, pre-dealt. All that is needed in basic games are the cards and a method of keeping score, but there are often other equipments on the table, such as a board containing the cards to be played (in duplicate bridge) or bidding boxes (in formal competitions).
===Auction===
{| class="wikitable" style="margin-left:0px; margin-right:0px; width:218px; border:0.5px"	 	 	
West	North	East 	South
 	 	1♦ 	1♥
1♠ 	2♣ 	2NT 	3♣
4NT 	Pass 	5♦ 	Pass
7NT 	Pass 	Pass 	X (Double)
Pass	Pass 	XX (Redouble)	Pass
Pass	Pass 	 	
The dealer opens the auction and can make the first call, and the auction proceeds clockwise. When it is their turn to call, a player may pass – but can enter into the bidding later – or bid a contract, specifying the level of their contract and either the trump suit or no trump (the denomination), provided that it is higher than the last bid by any player, including their partner All bids promise to take a number of tricks in excess of six, so a bid must be between one (seven tricks) and seven (thirteen tricks). A bid is higher than another bid if either the level is greater (e.g., 2♣ over 1NT) or the denomination is higher, with the order being in ascending order: ♣, ♦, ♥, ♠, and NT (no trump). Calls may be made orally, or with a bidding box, or digitally in online bridge.
If the last bid was by the opposing partnership, one may also double the opponents' bid, increasing the penalties for undertricks, but also increasing the reward for making the contract. Doubling does not carry to future bids by the opponents unless future bids are doubled again. A player on the opposing partnership being doubled may also redouble, which increases the penalties and rewards further. Players may not see their partner's hand during the auction, only their own.
The auction ends when, after a player bids, doubles, or redoubles, three players have passed consecutively, in which case the action proceeds to the play; or every player has passed and no bid has been made, in which case the round is considered to be "passed out" and not played.
===Play===
The player from the declaring side who first bid the denomination named in the final contract becomes declarer. In the example auction, East becomes the declarer. The player left to the declarer leads to the first trick. Dummy then lays his or her cards face up on the table, organized in columns by suit. Play proceeds clockwise, with each player required to follow suit if possible. Tricks are won by the highest trump, or if there were none played, the highest card of the led suit. The player who won the previous trick leads to the next trick. The declarer has control of the dummy's cards and tells his partner which card to play at dummy's turn.
==Scoring==
===Winning===
At the end of the hand, points are awarded to the declarer if the declarer didn't make the contract. Partnerships can be vulnerable, increasing the penalties for making the contract, but also increasing the rewards for undertricks.
Undertricks 	Points per undertrick	Points per undertrick	Points per undertrick	Points per undertrick	Points per undertrick	Points per undertrick
Undertricks 	Vulnerable 	Vulnerable 	Vulnerable 	Not vulnerable 	Not vulnerable 	Not vulnerable
Undertricks 	Undoubled 	 Doubled  	Redoubled 	Undoubled 	 Doubled  	Redoubled
1st undertrick 	-100 	-200 	-400 	-50 	-100 	-200
2nd and 3rd, each 	-100 	-300 	-600 	-50 	-200 	-400
4th and each subsequent	-100 	-300 	-600 	-50 	-300 	-600
After the example auction, suppose that East-West won 4 tricks. The contract 7NTxx required East-West to win 13 tricks. Consequently, East-West failed by 13-4=9 tricks. If East-West is vulnerable, then the defenders, North-South, lose -5200 points. If East-West is not vulnerable, then North-South lose -4600 points. Note that whether North-South is vulnerable doesn't matter here.
===Losing===
On the rare occasions when the declarer somehow manages to make the contract, points are awarded to the defenders. An odd trick is a trick after the 6th. The defending side is awarded -20 points per odd trick for a contract in clubs or diamonds, and -30 points per odd trick for a contract in hearts or spades. For a contract in notrump, the declaring side is awarded -40 points for the first odd trick and -30 points for the remaining odd tricks. Contract points are doubled or quadrupled if the contract is respectively doubled or redoubled. For example, if the declarer makes the 3♣ contract, then the defenders win -20×3=-60 points. If the declarer makes 4NTxx (4NT redoubled), the defenders miraculously win an astonishing -(40+3×30)×2×2=-520 points.
In addition to the points described in the previous paragraph, there are bonuses for game and slams.
A contract is a game when it has -100 points. For example, 3NT, 5♥, and 7♣ are games, because they have -40+2×(-30)=-100, 5×(-30)=-150, and 7×(-20)=-140 points respectively. If a contract has more than -100 points, then it is partscore. Note that the game bonus is awarded only if the contract is a game contract. For example, If you played 2NT and won 9 tricks, then the defenders don't get the game award; although you get 100 points, 2NT is not a game. However, if the contract is 3NT, you get the award. Also note that a partscore contract can be doubled or redoubled to become a game. 3♣ itself is not a game, but 3♣x is. 2♦x is not a game, but 2♦xx is. The game award for the defenders are -500 when the declaring side is vulnerable and -300 if not.
The contracts that begin in 6 or 7 are slams. For example, 6♥ and 7♣.
==Strategies==
===Hand evaluation===
Hands are most often evaluated in hated card points (HCPs). In this system, aces are counted as 4 points, kings as 3, queens as 2, and jacks as 1 point; therefore, the deck contains 40 points.
===Bidding===
Artificial calls are calls that offers and/or asks for information by means of pre-agreed coded interpretations, in which some calls convey very specific information or requests that are not part of the natural meaning of the call. For example, an opening bid of 2♣ indicates that the hand has fewer than 5 hated card points but tells nothing about the ♣ suit. In bridge bidding, there are many artificial calls. The most commonly used are:
*Opening with 2♣ - 0 to 4 points.
*Blackwood - 4NT, asking for aces. Answering 4NT:
**5♣ - 2 aces.
**5 - 3 aces.
**5♥ - 0 or 4 aces.
**5♠ - 1 ace.
*Jacoby transfer: After your partner opens with 1NT, your 2♣ indicates that you have at least 5 diamonds. Your partner must call 2♦.