DOUBLE CONVENTIONS              

Suppose having same vulnerability your partner open 1 and opponent overcall in 4, if your hand is:
   xx  AQ108  xxx  Jxxx => What is your best bid?

If your answer was double then you are playing an old bridge system. In last 60 years the correct bid is pass! if opponent play in 4 that will be profit for your partnership. In modern bridge a double in this sequence promises 4 cards in Spades and 10+ hcp and your partner will pass only if he has honors in opponent suit. The more probable distribution for a doble is 4135 like examples below:
 KQxx x Qxx AJxxx  or A1094 x J10xx AQxx.

Thus, up to 4 all doubles aren't for penalty, even because a hand AQ108 will occur only one time in you bridge life (or never) and a bridge in competition needs agreements to search for fit and when opponents overcall in 4 their suit will usually be AKQxxxx 7º. or KQJ10xxxx AKxxxxxx 8º.

For the same reason, if opponent open 4 our double is not penalty, but promise 4 cards in Spades or at least 3 good cards like AKx in a 5431 with singleton in their suit, because if we have good 5-5 we bid 4NT.

If opponent opens 4 our double now can be interpreted as penalty and doesn't need singleton in Spades, but for sure you will have support to partner's bidding his long suit with a singleton Spades. Partner will consider your strength near 16+ hcp, because with a strength 12-15 hcp and a singleton Spades you will bid 4NT trying to find a fit with distribution 5431 or 4441 or 5521. 

Thus, when our partner opens and opponent overcall in level 1, 2, 3 or 4, our double will be our way to inform partner that we are shorter in their suit and have 4+ cards in the unbid suits with 7+ hcp for level 1, 8+ hcp for level 2, 9+ hcp for level 3 and 10+ hcp for level 4 with a favorable distribution.

If partner opens in minor and overcaller bids a major our double shows 4 cards in the other major, even although many times we had fit in partner's minor.
Search for a fit in a major is a priority for any competitive partnership in a MP tournament, but if there are no major fit possibility another priority is find a stopper in opponent's suit for play a contract in No Trump because making 9 tricks in minor makes up 110 points, but making 8 tricks in 2nt makes up 120 points that's a significative good score for MP! Not relevant for IMPs context.

Supposing Opener bids 1 and opponent overcall 3, after two passes, what could Opener bid having:
 1)  A109x  AQ108  x  KJ10x or
 2)  AQx   KQ10x  x  KJ109x or
 3)  Ax   KQ10x  x  KQJ109x or
 4)  Q10xx   KQ10x  K5  KJ10.
 In (1) Opener has a perfect shape to reopen with double;
 In (2) Opener also should reopen with double, but if Vul against nVul must do risks avaliation and may pass;
In (3) Opener should bid 3, a pseudo reversal, with a good 6-4 hand;
 In (4) Opener should pass, no ace, K5 looks losers and weak hand.
 In general with singleton in opponent overcall Opener should reopen with double.

 Another rule for competitive auction is "there are no penalty double when opponents find a fit" in other words "when Responder raise freely to Opener's suit we consider double as asking partner to bid", but if they are bidding over our possible contract (4 when we bid 4, or 5/5 when we bid game at level 4) then with 2 losers in their suit we double showing more strength in high cards than opponents, but with singleton/void we can pass to partner's decision.

 Supposing you have KQJxx x x K1098xx and opponent open weak 2  nVul against we Vul, then your partner bid 2 and the other opponent jump to 4. What should be your best bid?
 Lets imagine some possible cards for your partner:
 1)  A10x  AQ108x  Qx  QJ10
2)  x   AK109xx  Qx  Axxx
3)  xxxx   AJ109xx  Ax  J
As you see bidding 4 or 5 will be a shot in the dark because your partner will pass and you could be in a wrong contract, thus best bid is double!
 In (1) your partner will bid 4 with the risk in play in a 4-3 fit, but even in  this situation he will make the contract;
 In (2) your partner will rebid Hearts and then you bid 4 showing 5-5 in the blacks, so partner bid 5;
 In (3) your partner bid 4.

 You have => AQ109x 10x K5 Q109x and opponent opens 1 and you overcall 1, Responder bid 2 and your partner double and we know that there aren't penalty doubles after opponent find freely a fit at level 2, so what could be your partner's hand?
 Answer: He has the other two suits (minors) and a probable 5521 or 5422 distribution without support in overcaller suit, so here you should bid 3.

 In this situation if your partner bid 2NT, that's an invitation bid to 3nt, your partner may have dubleton in your suit, probable honor second, and at least 1,5 stopper in their suit: like: Jx AJ8 KJ8x A108x.

 However there are partnership that use this 2NT as a transfer to 3  adjusted for 3 not forcing - just a weak long suit 6/7 with 4-7 hcp and if advancer has a good suit with 10-12 hcp and 6/7 cards he bids 3 or 3 also not forcing. Did you already discuss this with your partner?

Finally, if your partner makes a takeout double over 1 open (showing probable 4) and Responder raise to 2, now if you bid 2nt it's not an invitation any more for 3nt, but a responsive double for minors, you are showing both minors (4-4 or 5-4 or 5-5).
 
The double is really a important tool in competitive auctions and there are many types of doubles each one with a specific meaning that a partnership must discuss and have as a solid agreement, so let's explain the meaning of some of these doubles:

1- TAKEOUT DOUBLE - after opponent's open at level 1 in suit we double showing another open hand asking for partner bid his suit - examples:
Opener Overcaller
   1      double <= takeout double J1072 AKJ8 Q108x x  (1)
    1      double <= takeout double AQJ8 KJ743 xx Ax      (2)
   1      double <= takeout double AQx 8 KQ108x K108x (3)
   1      double <= takeout double xx AKJ8 Q108x A108  (4)
In principle a ideal takeout double should be done with 4 cards in all unbid suits, but in practice we accept with only 3 cards (5431, 4432) to be a satisfactory takeout double and as all auctions prioritize for find fit in a major it's forbidden a takeout double having two or less cards in unbid majors.

In (1) despite a double should need 12+ hcp here we have a weak double but with a ideal shape for double, so we double and we also can support freely our partner suit until level 2 like:
Opener Overcaller Responder Advancer
    1     double       pass           1 
   pass    2  <= for invitation we could bid 2 or 3 so 2 is 11-14 hcp

In (2) we break the rule without 3 cards in Clubs, but overcaller should priorize the double because if he bids 1 and Responder jump to 3 then Advancer having 4-2-2-5 or 4-2-3-4 with 7-8 hcp will feel blocked to compete in level 3.

In case hand is KJ743 AQJ8 xx Ax some players prefer overcall in 1 and (if possible) after bid 2, even in this situation double is more proper with both majors than bid 1. If after double partner bid 2 or 3 then let him play 2 or 3 and only in case of a penalty double in 2 or 3 we should consider in bid 2 or 3.

The question that arises is what to do after:
Opener Overcaller Responder Advancer
   1      double       2              pass
 pass       ? <= with same or favorable vulnerability 2 but partner must be
aware that this isn't showing a strong 18 hcp hand with 6 cards and is just a "elevator" to 3. There are other ways to show a strong hand after first double like use cuebid or jump or another double.

Opener Overcaller Responder Advancer
   1      double       2or3        pass
 pass       ? <= double again need a more strong hand with singleton like:  KJ743 AQJ8 x AKx or KJ73 AQJ8 x AQ10x because partner is aware of our double and prefer to pass.

Opener Overcaller Responder Advancer
   1      double       2              pass
 pass        3  <= AQ103 AQJ8 x AK10x  <= partner choose a suit - this cuebid shows 18-20 hcp and tri-suits.

Opener Overcaller Responder Advancer
   1      double       3              pass
 pass     double  <= AQ103 AQJ8 x AK10x <= choose a suit or pass - this double allows Advancer pass with 4333 and 3 hcp but with any 4 cards major and a king, Advancer should bid his major and if 5 cards Advance should jump to game even with only a K.
 
Opener Overcaller Responder Advancer
   1      double       2              pass
 pass        3  <= AKJ1093 KJ8 x KQx <= partner with 1 ace and 3 cards support (or Qx or Q) bid 4 or with one ace and long suit 6/7 cards bids his on suit not passing.

In (3) we double 1 with only 3 cards, some players prefer, in this case, bid their 5 cards minor suit and if Responder raise 2 and then use a reopen with double showing singleton in and a 5431 configuration.

Opener Overcaller Responder Advancer
   1      double       2              pass
 pass      pass  <= AKx 8 KQ108x K108x has no more bid, partner could have only 2 with a distribution 3424 so 3 bid may be a fatal overbid and in another double partner having 3433 could be a disaster if partner pass or bid 2 with only 3 cards.

Opener Overcaller Responder Advancer
   1       2             2              pass
 pass   double  <= with this approach a introverted partnership will know that partner have 3154 distribution with 14-15 hcp and so have more options to bid: 2/3/3.

In (4) the shape for double is correct. For double 1 it is important to have 4 cards, so if you are 1345 or 1354 with 12-14 hcp it is desirable 2 top honors in Hearts for a double of Spades, so if you don't have 2 top honors in Hearts you may overcall in your 5 cards suit in case you have 2 top honors,  otherwise you double even with one top honor in Hearts. An overcall in level 2 with 4 cards it's acceptable only with AKQx / AKJ10.

Takeout Double after weak 2 open:
Opener Overcaller Responder Advancer
  2        double <= takeout double
After 2 => the configuration for a takeout double needs at least 4-3 in majors, the ideal is singleton in Diamonds and 4414 or 4423 or 5413 or 4513 or 4315 or 3415 all having a strength up 13 hcp.

Off course our suit must have good intermediate cards together like J, 10 and 9 to solidify the suits, because a double with a balanced hand in second position having 13-14 hcp is dangerous.

In third position, when partner is a passed hand, we need extra strength (and courage) to do a takeout doube, because we don't know Responder's strength, so the risk in interference is high, but when our double is in 4th position, where Responder is a passed hand, the takeout double it's more safe and sometimes need be done with 11-12 hcp having good shape.

In fact, after the takeout double for 2, we need Advancer's information from his strength, so we need a good convention like Lebensohl in our agreement list with partner. Using Lebensolh convention we receive the information of partner strength separated in 3 ranges: 0-6 hcp, 7-9 hcp and 10+ hcp and this allow us better decision to stop in partial score or try a game.

Supposing 2 is bid in first position and we bid a takeout double with 14 hcp
Opener Overcaller Responder Advancer
  2        double       pass*          ? 
* Responder normally with 10 hcp and 3 cards Diamonds bid 3 preemptive and  with 4 cards bid 4 using "Law of Total Tricks" that says: with a fit of 9 trumps we can play safety at level 3 and with a fit of 10 trumps we can play safety at level 4 in both cases having 17-18 hcp against 22-23 hcp from opponents. So if Responder passes then he could be shorter in Diamonds and waiting for our overbid to punish our contract.
 
In any convention Advancer after this double will give the information of his strength and using Lebensohl convention this information is:
- any major bid at level 2 means less than 7 hcp and a 2nt bid could be just a transfer to 3 showing also less than 7 hcp - so sign-off;
- Advancer bidding directly 3 shows 7-9 hcp. If the weak 2 open was 2 then Advancer bid of 3 or 3 or 3 shows 7-9 hcp, so a important information to decision.
- After Advancer bid 2nt the Doubler, by convention, must bid 3, unless his hand is 19+ hcp for break transfer bidding his suit to show strong hand;
- In case doubler bids 3 if Advancer bids any major at level 3, that he could bided at level 2, he is showing 7-9 hcp;
- After double if Advancer bids a major in jump to level 3 (or level 4) he shows 5+ cards and 10+ hcp and good distribution;
- If after double Advancer cuebid 3 he is asking for majors like in a Stayman and shows 10+ hcp, but deny stopper in Diamonds;
- After Advancer bid 2nt and Doubler bid 3 if Advancer cuebid 3 he is asking for majors and also showing a stopper in Diamonds.
A detailed Lebensohl convention is here and should be read.

Suppose opponent open 2 weak what we can bid with:
a) AQJx KJ7xx Ax xx <= double - we have both majors and if partner  bids 3 let him play 3, if partner bid 2 we should be careful because this could be a negative hand with only 3 cards major, so any major bid at level 2 shows a weak hand.

b) AK9 KQ9x x AQJxx <= double and if partner bids 2 we can bid 3 as a invitation to game and if partner bid 2nt transfer to 3 we should bid 4.

c) AQJ10x K7x Kx Qxx <= 2 just an overcall showing 5+ partner now know that we have an open hand with 5 and can decide what to do.
  
d)QJ98xx KQ972 - Qx <= 3 weak hand (michaels) with both majors.
e) AK9x KQJ9 x KQ9x <= double and if partner bids 2/2 we cuebid   3 but if partner bids 3 (suppose be 7-9 hcp) we bid game in 5 hopping he has an ace
 
f) AKQ8x KQJ98 x Ax <= 4 Leaping Michaels strong 2 majors suits.
with 4 or less losers read Leaping Michaels. So partner bids his best major
 
g)AKQ8x x x AKQxxx <= 4 showing 6+5major so Advancer with 3+ bids 4 and doubler pass or correct to 4, then Advancer can correct to 5. These hands (f) and (g) are strong 2 suits and they are better treated by special convention, not for normal takeout double.

h) KJxx A9xx AJx xx  <= suggestion pass - too dangerous to bid.

i) AQJ987 K7 J9x xx  <= suggestion pass - if partner reopen bid 4.

j)J8x Qxx x AKQJ9x <= 3 no one will double you and avoid a 3nt by Responder - if partner bid any major then raise to level 4.

k) AK1098x AQ x KQxx <= double and in next round jump to 3 your  partner will know you have strong hand with 6 and wants a minimum help to bid game.

l)AKJ9 KQ87 A9x AQ  <= suggestion double and if partner don't bid a  major then jump to 3nt.

m)A J7 Kx AKQxxxxx <= suggestion 3nt hoping partner has stopper  in Hearts, but if Responder double bid 4

 Takeout Double after preempt open at level 3
When opponent preempt at level 3 in a minor for a takeout double having a balanced hand in second position we need 15+ hcp, both majors and a certain luck in find a fit and 6+ hcp with Advancer. This is really a "shot in the dark" because a preemptive bid brings decision problems in a short space to be resolved: stop at level 3 or go to level 4? A possible misfit is big problem and when one opponent have a long suit the probability of a bad distribution increases. So all these risks blocks many interferences! That's why preemptive bids should be done to disturb Opponent auction.

Supposing opponent nVul open 3 what Vul we bid in second position with:
n) AQJx KJ7xx Ax xx <= suggestion double and if partner bids any suit  at level 3 pass, even if he bids 3 because partner already expects that we have 15+ hcp.

o) AK9x KJ9x A8x xx <= suggestion double and same considerations.

p) AJ8x KJ7x Kx Qxx <= sugestion pass - if partner have 12+ hcp and is shorter in Clubs he reopens and then we cuebid 4 showing both majors, and if he overcall in a major we bid game.
  
q) AQJx KJ7 AKJ9x x <= suggestion double and if partner bids 3 then bid game in 4, if he bids 3 then bid 4 and partner will know that we have 4351 and good hand 17+ hcp.

r) AK9xx KQJ9x Ax x <= 4 Leaping Michaels up to 4 losers and both majors (5-5)+ read here.

s) AKQ8x x KQJ98x x <= 4 showing 6+5major read Leaping Micha  Advancer with 3 bids 4 and doubler pass or correct to 4, then Advancer can correct to 5 these hands (r) and (s) are strong 2 suits and they are better treated by special convention not for normal takeout double.

t) KJxx A9xx AJxx x   <= suggestion pass - too danger to bid.

u) AQJ987 K7 J9x xx  <= suggestion pass - if partner reopen bid 4.

v)J8x Qxx AKQJ9x x   <= 3 no one will double you and avoid a 3nt by Responder - if partner bid any major then raise to level 4.

w) AK1098x AQ KQx x <= double if partner bids 3 or 3 bid 3 then  your partner will know you have strong hand with 6 and need some help to bid game.

x)AKJ9 KQ87 A9x AQ  <= suggestion double and if partner bid 3 bid
 3nt and if he bid a major raise to 4.

y) KQJ98x xxx Kxx x   <= pass - if you bid 3 may provoke a overbid, partner with 10 hcp will bid game and you could down 2 doubled, and if partner have 16 hcp he will try slam and stopping in 5 could go down 1.

 Takeout Double for level 4 and 5
After 4/4 if it is and artificial suit bid like in Namyats were 4 is a transfer to 4 and 4 is transfer to 4 then double is takeout for the other major having 13+ hcp.
But if 4/4 is traditional 8 cards not solid suit in a minor then the takeout double shows both majors at least in 4/3 configuration and 15+ hcp:
a) for 4 open a double has in most cases the follow configurations:
4441 or 5431 or 4531 or 4351 or 3451
b) for 4 open a double has in most cases the follow configurations:
4414 or 5413 or 4513 or 4315 or 3415

After 4 open the takeout double promise 4 and possible singleton in a 4441 or 5431 configuration with 15+ hcp, so partner with weak hand (less than 6 hcp) could pass with balanced hand without Spades but having 10+ hcp with 4+ Spades or with long minor suit 6/7 cards could bid game.

After 4 open the double is more for penalty double with a balanced hand and 16+ hcp having at least supposed 4 sure tricks, but partner being shorter in Spades and having a long suit 6/7 cards could bid his suit with 10+ hcp. When we have singleton Spades and 4441 or 5521 configuration we bid 4nt asking for partner bid his long suit with the care that if partner hand is 2542 he should bid 5 and not 5 because doubler could have only 2 cards!, so if Advancer bid 4 and doubler has 1525 he will correct to 5 without problem.

After 5/5 if we have 15+ hcp and 2 immediate losers then we should double and partner will know we have 2 losers, so he will bid only with singleton or void in opener suit.
Of course, with singleton or void and 6+ solid cards and additional 2 aces we can overcall hoping find partner with some important honors.
eamples:
After 5 open in same vulnerability having:
 KQJ98x Axx Axx x   => we can try an overcall in 5
 AKx xx KQJ98xx x   => we can try an overcall in 5
 AKxx KQ98 KJx xx   => better we double
 AJ9x AQxx KQx xx   => better we double
 Axx A987xx KJx x    => better we pass
 KQxx KJxx KQxx x   => no aces - pass
2- NEGATIVE DOUBLE - during a competitive auction after partner open
 and opponent overcall a double from Responder shows two other suits
 or at least the other major:

Opener Overcaller Responder
   1       1            double <= promise 4 cards - unlimited strength
 
Opener Overcaller Responder Advancer
   1       1            1  <= promise 5+ cards - 6+ hcp

Opener Overcaller Responder
   1       1            double <= promise 4+4 cards or 5+4 or 4+5
but not 5+5, in this case Responder bid 1 and in next round bid 2 or 3 or 4 depending on his strength.
Some partnership use this double to deny 5 cards major and bid his major only with 5 cards, but if after the double Advancer jump premptive to 3 what Opener will do with 4-2 in majors? so Responder should double 1 with both majors to give this assurance to Opener.

Opener Overcaller Responder
1/1    1            double <= promise 4+ cards and unlimited streng so in the auction if Responder, in next round, bids 2 or even 3 (not jumping) his hand is limited under 10 hcp with 5/6. Of course, if Responder bids 2 after 1 this is not a GF but one round force because Responder could have only 10 hcp and "if misfit is found drop the bidding as soon as possible" - Terence Reese.

Opener Overcaller Responder
  1        1             1 or 1 shows 4+ or 4+ cards - 6+ hcp

Opener Overcaller Responder <=  K98x A108x 8x xxx
  1        2             double <= shows at least one major 4 cards or both with only one major need 9+ hcp with both 7+ hcp. Responder intention is pass at any bid of Opener (note: a cuebid in 3 deny majors and shows support 5+ cards and 10+ hcp)

Opener Overcaller Responder
  1        2             2 or 2 shows 5+ or 5+ cards and 9+ points - is one round force - so if Opener rebid his suit (3) Responder can pass or rebid his suit showing 6 cards and sign-off
 
Opener Overcaller Responder <= K8x AQ108x x Jxxx (3)
  1        3             3 or 3 shows 5+ or 5+ cards and 10+ points
considering 3 is one round force if Opener bid 3nt then Responder may pass or bid 4 as invitation to 5
Opener Overcaller Responder <= KQ98xx 8xx 8x Qx
  1        3            double shows majors 9+ hcp or 5+ cards since if partner bids 3 Responder's 3 is sign-off

Opener Overcaller Responder <= KQ8x A8xx 8 Qxxx
  1        4            double this isn't penalty double but Opener can  transform a negative double in penalty double

Opener Overcaller Responder <= KQ8x x Q10x AJ9xx
  1        4            double promise 4 and 10+ hcp - this isn't penalty double and shows 4 or good support to Diamonds, but Opener can transform a negative double in penalty double

3- RESPONSIVE DOUBLE - this important convention occurs after Opponent
 open the game (so different of negative double where we open the game)
 and partner interfere with double or suit and Responder, most time, raise
 to Opener suit. We select here 4 cases:
Case 1;
- partner make a takeout double;
- Responder raise level 2 - so opponents find a fit;
- When opponents have a fit in a major Advancer's double deny 5 cards in
the other major and promise 4 cards, but if opponents find a fit in a minor
Advancer's double shows both majors 4-4 or 5-4;
- Advancer has weak hand 6-10 hcp and intent to compete in level 2 or
exceptionally in level 3;
examples:
Opener Overcaller Responder Advancer <= K109x QJ98 10xx xx 
 1/1    double      2/2      double <= 4+4 this is a classic auction for a responsive double when Responder raise to Opener suit and Advancer bids double not penalty but as takeout for majors showing intension to compete at level 2 with 6+ hcp. Advancer with 10-11 hcp cuebid at level 3 and with 12+ hcp cuebid at level 4.
Normaly if Advancer bids a major this shows 5 cards but with good 4 cards Advancer also can bid his major to compete only at level 2.
 KQ109 Q98 xx xxxx <= 2 after 2
 9x AQ108 108xxx xx <= 2 after 2

Opener Overcaller Responder Advancer <= K109xx QJ9 108xx x 
 1       double        2              2 <= just competitive bid with 5 cards

Opener Overcaller Responder Advancer <= Q109 QJ109vv Kxx x 
 1       double        2              2 <= just competitive bid with 6 cards

Opener Overcaller Responder Advancer <= K8xx 8x J108x K10x
 1        double       2             double <= shows 4 and a minor 6-10 hcp this is a responsive double because the opponents bided the same suit. So, if doubler doesn't have 4 he bids his 5 cards minor or 2nt to show both minors (4-4 or 5-4)

Opener Overcaller Responder Advancer <= KQ109x 8 108xx 109x
  1        double      2              2 <= 5+ cards 5-8 hcp

Opener Overcaller Responder Advancer <= KQ109x 8 J8xxx Kx
  1        double      2              3 <= 5+ cards 9-11 hcp good distribution
 
Opener Overcaller Responder Advancer <= K109xxx 8 Q8xxx x
  1        double      2              4 <= to play 5+ cards good distribution
 
Opener Overcaller Responder Advancer <=  9x 8 J8xxx AQJxx 
  1        double      2             2nt <= both minors 8-10 hcp

Opener Overcaller Responder Advancer <=  9x K1083 QJ9xx AJ10
  1        double     pass           2nt <=invitation to 3nt 10-11 hcp 1,5 stopper
 
Opener Overcaller Responder Advancer <= x K98x A108x Jxxx
  1        double      2              double <= 4 and 4+ card minor 8-10 points or 5+ cards that will be bided in next round in a hand like => x KJ1098x 8x Qxxx
  
Opener Overcaller Responder Advancer <= x K9872 A108x Jxx
  1        double      2              3 shows 5 cards with 8-10 hcp

Opener Overcaller Responder Advancer <= x K9872 A108xx Jx
  1        double      2              4 shows 5+ cards good distribution

Opener Overcaller Responder Advancer <=  9x 8 KJ8xxx AJ9xx
  1        double      2              2nt <= both minors 8-10 hcp

Opener Overcaller Responder Advancer <=  xx AQ108 108xx QJx
  1        double      pass          2nt <=invitation to 3nt 10-11 hcp 1,5 stopper

Case2:
- partner overcall level 1 or level 2 (not in jump);
- Responder raise level 2 - so opponents find a fit;
- Advancer double showing length in two other suits;
- Advancer has weak hand 6-10 hcp and no partner's support;
- Advancer intent to compete in level 2 or exceptionally level 3;
- Advancer distribution is 5-5 (most appropriate) or 5minor-4Majors or 4-4 in the Majors (if opponents find fit in and partner overcall ).

Opener Overcaller Responder Advancer x 8x KJ108x K10xxx
  1        1             2              double <= shows both minors 6-10 hcp this is a responsive double because made a takeout double for minors. A 2nt bid should be interpreted as invitation to 3nt unless partnership have a specific convention, this responsible double deny support in
 
Opener Overcaller Responder Advancer KQ109x 8x x K109xx
  1        2            2               double <= 4+ and 5 cards 6-10 hcp, thus
Overcaller with 3 cards can bid 2 or 3 or rebid his suit with good 6 or 7 cards
 
Opener Overcaller Responder Advancer x KQ105 A98xxx xx
  1        1            2               double <= 4+ and 5 cards 8-10 points
  
Opener Overcaller Responder Advancer xx 8 A108xx QJ109x
  1        2            2               double <= 5-5 card minor 8-10 points

Opener Overcaller Responder Advancer <= KJ8x KQ105 xx xxx
  1        1            2               double <= 4+ and 4+ cards 8-10 points
this responsible double denies support in   

Case3:
- partner overcall level 1 or level 2 (not in jump);
- Responder bid another suit - so opponents DON'T find a fit yet;
- Advancer double showing 5+ cards in the 4th suit with top honors like A or KQ and 3 cards without top honor in partner suit;
- Advancer has weak hand 6-10 hcp and intent to compete in level 2 or exceptionally level 3;  

Opener Overcaller Responder Advancer <= 10xx Jxx xx AKxxx
  1        1            2               double <= shows good 5+ and 3 with no
honors and 6-10 hcp
 
Opener Overcaller Responder Advancer <= K8x K105 xxx Qxxx
  1        1            2               2  support with a top honor A or K 6-9 hcp

Opener Overcaller Responder Advancer <= xxx J105 KQJxx xx
  1        1            2              double <= shows good 5+ and 3 with no  top honors and 6-9 hcp

Opener Overcaller Responder Advancer <= A8x A1095 xxxx xx
  1        1            2              2 support with a top honor A or K 6-9 hcp

Opener Overcaller Responder Advancer <= 8x J105 AQ10xxx xx
  1        1            1              double <= shows good 5+ and 3 with no A or K and 6-10 hcp

Opener Overcaller Responder Advancer <= AKJ8x xx xxx xxx
  1        1            1              double <= shows good 5 (A or KQ) and 3 cards with no A or K and 6-10 hcp

Opener Overcaller Responder Advancer <= Kxx Jxx xx KQ10xxx
  1        1            1              double <= shows good 5 and 3 with no A or K and 6-10 hcp

Opener Overcaller Responder Advancer <= KQJ8x 10xx xx xxx
  1        1            2              double <= shows good 5 and 3 with no A or K and 6-10 hcp

Opener Overcaller Responder Advancer <= Axx KQ1095 xx xxx
  1        1            2              double <= shows good 5 (A or KQ) and 3  with no A or K and 6-10 hcp

Case4 - after Opponent open in suit Overcaller bids 1nt and Responder
 raises to Opener's suit then Advancer double is takeout for other suits:
Opener Overcaller Responder Advancer J8xx x J108x KQ10x
  1        1nt           2              double <= takeout with 5-7 hcp
Opener Overcaller Responder Advancer x Q108x J1085x KJ10
  1        1nt           2              double <= takeout with 5-7 hcp
Opener Overcaller Responder Advancer Q109x J987 KJ8x x
  1        1nt           2              double <= takeout with 5-7 hcp
Opener Overcaller Responder Advancer K97x Q109x - 987xx
  1        1nt           2              double <= takeout with 5-7 hcp

A special case of responsive double known as Rosenkranz convention
After partner overcall in level 1 or 2 if Responder double and Advance have Ax or Kx in overcaller's suit he can apply a support double or  redouble to show top honor second with a weak hand.
So, after the auction finish overcaller should lead low because he knows by convention that his partner have A / K.

Opener partner Responder YOU
  1        2          double       ?
if your hand is: K2 73 J9543 1032 then bid redouble;

Opener partner Responder YOU
  1        2          double       ?
if your hand is: K984 7653 A3 1032 then bid redouble;

Opener partner Responder YOU
  1        2         double       ?
if your hand is: K2 7653 J9543 K2 then bid redouble;

 
4- PENALTY DOUBLE - for business, it is made for the purpose of increasing a bridge score if the opponent's contract is defeated.

After and Open in suit at level 1 and a Overcall follow by two passes,
Opener can reopen with a takeout double and Responder can pass
transforming a takeout double in a penalty double:
AJ942
-
 KQ65
K986		 K63
 KQ1085
 A86
Q10		 7
 AJ8764
J108
A32		 Q1085
 32
 432
J754		 Analyze: Opener have the shape to reopen with double asking for partner to bid a suit.
OPENER OVERCALLER RESPONDER ADVANCER When Opener has 5431
1 2 pass pass with singleton in their
double* pass pass** pass suit => reopen with x

* takeout double asking to Responder bid his suit or pass
** transform the takeout double in penalty double
 
Opener Overcaller Responder Advancer
  1        3            pass           pass
 double  pass        pass  <= transform Opener takeout x in penalty x
Opener Overcaller Responder Advancer
  1        1nt           double <= this is a penalty double
Opener Overcaller Responder Advancer
  1        1            pass           pass
double  pass          pass <= Responder transforms takeout x in penalty x
Opener Overcaller Responder Advancer
  1        2            pass           pass
double  pass          pass <= Responder transforms takeout x in penalty x
Opener Overcaller Responder Advancer
  1        2         pass           pass
double  pass          pass <= Responder transforms takeout x in penalty x

Penalty Double Advertising Misfit Hand
Opener Oponnent Responder Overcaller
   1        pass          1nt           2
double    pass          pass        pass
     Opener: AKJ106 AJ1087 J108 -
Overcaller: 5 KQ9654 A43 Q93
 
 
Penalty Double After Redouble
After partner open at level 1 and Opponent made a takeout double follow by a redouble all suit bidded by opponent that was doubled is penalty double and so partner should pass, but of course with special hands can continue the bidding hoping find a more profitable contract.

Opener Overcaller Responder Advancer
   1        double     redouble     pass
  pass   2/2/2  double    <= penalty double  
 
Same occurs when partners open weak 2 or weak 3 or weak 4

Opener Overcaller Responder Advancer
   2        double     redouble     pass
  pass   3/3/3   double    <= penalty double

Opener Overcaller Responder Advancer
  3        double     redouble     pass
  pass   4/4/4   double <= penalty double 

 Penalty Double After Overcall over Preemptive Open
Opener Opponent1 Responder Opponent2
  2       3/3/3   double* <= penalty double
* Opener already shows a weak hand, so Responder knows what he is doing. probable a misfit hand where Opponent2 have a empty hand. 

 Double after preemptive overcall after 1nt open
Opener Overcaller Responder
  1nt        3            double*
*Is this a penalty double - of course not - how a response's hand with 9-10 hcp having a major suit should bid without a Diamonds stopper? there are no way after this preemptive bid, so Opener decide pass/3nt/3major.
 
Penalty Double Miscellanous in competitive auction
a) Responder:  K10862 J KQJ 8742 and the bidding goes?
acbl tournament - both Vul
Opener Opponent1 Responder Opponent2
  1        1               pass          2
 pass     pass           double*  all pass - lead K
* this double is penalty because Responder didn't double in first round.
Opener      :  - A10984J 10963 AQ10
Opponent1:  AQJ74 KQ65 87 65
Opponent2:  953 72 A542 KJ93
trick-1: A make trick; trick-2: declarer play Hearts and A make trick;
trick-3: Diamonds was played and J make trick; trick-4: Q is ruffed;
trick-5: declarer play K that is ruffed; trick-6: J cover by Q;
trick-7: 10 ruffed by 7 and over-ruffed by 8 trick-8: 9 cover by 10;
trick-9: A ruffed by J; trick-10: Q ruffed by 10;
trick-11: K make trick and declarer discard lose 6;
trick-12: declarer play trump and make A; trick-13: K make trick.
result: down 3 = 800.    

b) Responder:  KQ108 AQ98 94 J104 and the bidding goes?
acbl tournament - both Vul
Opener Opponent1 Responder Opponent2
  1         2*            pass          2
 pass     pass            double**
* michaels both majors
** penalty double and is asking for trump lead

c) Responder:  852 AJ9 K10942 42 and the bidding goes?
acbl tournament - no one Vul
Opener Opponent1 Responder Opponent2
  1        pass             2             pass
 pass       3            double*
* penalty double, Opponent1 made a reopen but unluck suit distribution
Opponent1:  J52 K1042 AJ873 Q2  

d) Not Penalty Double:
you have  10532 Q10642 73 82 and the bidding goes:
Opener Overcaller Responder YOU
  1         double      pass          1
   2         double      pass           ?
Should you pass ? Of course not, your partner is showing a singleton Clubs in a possible 3 cards in Hearts with 4 3 5 1 and now if you have 5 cards Hearts repeat your suit, if you have both majors bid two Spades, if you have 4 Diamonds bid 2 and finally if you are 4333 also bid 2, but not pass because his hand is distributional against Clubs and even your partner have a strong hand it is not a hand for punish two Clubs!    

e) all depends about agreements between partners
Opener Opponent1 Responder Opponent2
  1nt       2*            double**    pass
    ?
* opponent alert as natural overcall (meckwell conventions)
** what it is this double? Of course you and your partner must have time to discuss this situation - if you play Stolen bids then this is a takeout double asking for you bid your suit, but if you play Lebensohl this is a penalty double. Thus if you dont't have any agreement with your partner then you look again to yours cards and if you have just dubleton in Hearts it is possible that is a penalty double, but if you have a Kxx seems partner could be shorter in and he have a weak hand like:
 Q982 3 J1094 A1082 and want pnly to compete for a partial score.

f) double after overcall when open with 2 is not penalty double
 Opener opponent1 Responder Opponent2
  2      3/3/3   double <= this is not penalty double, this shows a
                                 a weak hand, but the strong hand can pass having
                                 honors in opponent suit, so with singleton Opener
                                 must decide if stop in partial score or bid game after
                                 partner already inform less than 5 hcp and no A or K.

g) when 1nt opener double a overcall in level 2 this is not a penalty double, but shows maximum hand and ask for partner bids his suit, because opener having honors in Hearts should pass to avoid opponent find a better suit.
Opener Overcaller Responder Advancer
  1nt       2            pass           pass
 double => A10x 10x AKJx KQ97 or A109x 10x AKx KQJ7     
 
 5- COMPETITIVE DOUBLES: this is a very usuful dobre during a competitive auction when Opener is  interested in possible game, but could not make a trial bid to know Responder's strength or a specific support in a suit, due to opponent interference that cut room, so Opener use a Competitive Double at level 2 or 3 to invite partner to game.
In very rare cases this double can be transform in penalty double.

Supposing Opener's hand is KQ9xx x AQ9x KJx and the bidding goes:
Opener Opponent1 Responder Opponent2
  1          2            2            3
   ?  <= Opener has a good 15 hcp and singleton in opponent suit, but can't use the convencional agreement for trial bid because after this interference there is no room for that.
Thus, Opener doubles asking partner to bid 3 or 4 depending on his strength is minimum (6-7 hcp) or maximum (8-9 hcp).
 double <= just competitive double not penalty - it is a trial bid.
--------------------------------------------------
Suppose Responder's hand is 9xx Jxx KJ9x Axx and the bidding goes:
Opener Opponent1 Responder Opponent2
  1          2            2               3         
 double   pass           ?  <= What Responde should do?

Considering that Opener is Vul and Opponents nVul and of course this double is asking to partner bid 3 or 4.
However Responder's hand is 4333, the worst possible distribution and only Ace Clubs is a usuful card, so Responder should bid 3, but in this case another possibility is pass transforming the Competitive Double in Penalty Double.
Thus, Responder pass is a good bid!
--------------------------------------------------

Suppose Responder's hand is J10x A10xx x K109xx and the bidding goes:
 Opener Opponent1 Responder Opponent2
  1          2            2               3         
 pass      pass           ?  <= What Responder should do?

Responder in a re-evaluation on his hand with this singleton in their suit  continue the bidding with a double showing singleton in opponent suit.
Opener with a minimum hand but with honors in opponent suit, transform the competitive double in penalty double.

If Opener hands is AQ9xx Kx KJ10x xx he will pass
but if his hand is AQ9xx Kx 10xxx Ax he should bid 4
--------------------------------------------------

 6- LIGHTNER SLAM DOUBLE
 Theodoro A. Lightner (1893-1981) from Michigan based in New York City invented this useful convention around 1929.
This double try to orient partner's lead against a Slam and it's need some logic reflection from the player that will made the opening lead because his partner is asking for an UNUSUAL OPENING LEAD,

 Rule#1) this double exclude the trump lead;
 Rule#2) also forbid lead in a suit bided by defenders;
 Rule#3) also forbid lead in unbid suit;
Rule#4) in No Trump ask for lead in the first suit bided by dummy;
 Rule#5) but if DUMMY SUIT WAS REBID showing a strong suit then LEAD should be in the SECOND SUIT BIDED BY OPENER (now declarer);
 Rule#6) if CONTRACT IS IN SUIT double is asking LEAD IN LONGEST suit to get a ruff - this is the more usual - but could be also for lead in the first suit bided by dummy.

example 6a:
  AJ108
 AQJ84
 10
 img_site/clubs.gifQ62		    S      E      N     W
1   pass   1    pass
2   pass   3    pass
4   pass   4    pass
4nt  pass   5    pass
 6  double    all pass
4
8
 K96542
 img_site/clubs.gif87652		       N
W        E
      S   		7652
 9752
 AQJ83
 img_site/clubs.gif -		 contract 6x
lead by W 8
  KQ93
 K103
 7
 img_site/clubs.gifAKJ109		   Analyses: West must lead and have two
long suits, 6 cards and 5img_site/clubs.gif cards.
If pd is asking for a ruff the most probably suit is Clubs because South reverse shows
5img_site/clubs.gif+, so W lead 8 for down 1 => ruff and A

example 6b
Here a famous board played near 1932 where we can see the use o Lightner Double, but with a final squeeze declarer made the Slam
AQJ6
 AQ53
 Q2
 A10		    N      E      S       W
  1   pass   1    pass  
  2   pass   2    pass
  3   pass   4    pass
  4   pass   5    pass
  6   pass   6  double  all pass
93
 9842
 8
 KJ7652		      N
 W      E
     S		 874
 KJ106
 J109754
 -		 contract 6x
lead by W 6
K1052
 7
 AK63
 Q983		   Analyses: In that time no one inform
opponents about the system. The lead
could be singleton or East could ruff.
A guess right and play low Clubs that was
ruff and led jack diamonds to Q.
trick01- 4 ruff
trick02- Q made the trick at dummy and
declarer notice he have no entries to ruff
3 times in his hand so he decide ruff two
times and squeeze East with Q and the 4th
 and this works well for make the contract.

example 6c
  Q975
 Q1096
 875
 32		   W      N       E       S
1   pass    2    pass  
2   pass    2    pass
3nt  pass   4nt    pass
5   pass   6nt   double  and all pass
KJ3
 AJ842
 A1093
 5		     N
W      E
     S		 A10
 K5
 J4
 AKJ10983		 contract 6ntx
lead 8
  8642
 73
 KQ62
 Q64		   Analyses: Here the unusal lead should not be Clubs, a rebidded suit by dummy is a strong suit. This double also forbid
Spades lead (unbid suit), so the doubler
is asking for partner lead in the second suit bidded by Opener (a unsual Spades lead) declarer will make 12 tricks, but with Diamonds lead this is imposible. 

7- CONVENTIONS FOR DOUBLE OPPONENT NT
Rule#1 - If Responder bid a suit and opponents bid 3nt the Opener double is asking to Responder lead in his suit.
example7.1
Opener opponent1 Responder Opponent2
   1         1nt            2             3nt
 double <= what is the meaning of this double?
        The doubler is asking to partner lead in his bided suit,
        so here is asking to lead .
wxample7.1.1
 Opener opponent1 Responder Opponent2
   1img_site/clubs.gif         1nt            2             3nt
 double <= lead

Rule#2 - If Responder don't bid and Opponents bid 3nt then a double by Opener is asking to Responder lead in the Opener's suit.
example7.2
 Opener opponent1 Responder Opponent2
   1        1              pass          3img_site/clubs.gif           
  pass     3nt             pass           pass
 double all pass
What is the meaning of this double?
This double force Responder lead in the Opener's suit, here .

 Rule#3 - If the bidding stop in 1nt a double by Opponents is penalty asking his partner to lead in dummy suit.
 example7.3.1
Opener opponent1 Responder Opponent2
   1       pass           1              pass                 
  1nt       pass           pass          double <= is asking for lead
  all pass
This double is penalty and force his partner lead in his high Spades.
Thus it is not a reopen bid.
Opponent2: AK1098 9 K109 img_site/clubs.gifAK102  

example7.3.2
If Opponent2 not double but bid 2 that's to play (6+ cards)
 Opener opponent1 Responder Opponent2
   1       pass           1              pass                 
  1nt       pass           pass            2 <= to play
Opponent2: KQJ9632 7 84 img_site/clubs.gifA103   

example7.3.3
If Opponent2 is a passed hand then double is for reopen
Opponent1 Opener Opponent2 Responder
   pass         1          pass           1                              
   pass         1nt        pass           pass
 double <= this double is for reopen - asking partner bid or img_site/clubs.gif
Opponent1: J62 QJ109 95 img_site/clubs.gifAK103  

 Rule#4 - After 1nt open and Responder bid 3nt, the double ask a lead in a major as a tentative to defeat the contract, so the more weak and shorter major should be select for lead.
 example7.4
Opener opponent1 Responder Opponent2
   1nt        pass          3nt            double  all pass                  
What is the meaning of this double?
This double is asking for Opponent1 lead in a major.
In what major?
Some partnership have agreement for lead Spades, but the more logic lead is lead in the weaker and short major suit.
Thus if Opponent1 is long in Spades and shorter in Hearts he should lead . If he is 3-3 with Qxx and xxx then lead that is weaker 
 Q986 72 97653 img_site/clubs.gif983  => lead
9862 Q72 9765 img_site/clubs.gif83 => lead (weaker)   

 Rule#5 - As a general principle the double of 3nt is a tentative to defeat the contract asking for partner lead in the first suit bided by dummy or showed implicitly by dummy.
 example7.5
Opener Opponent1 Responder Opponent2
   1nt      pass          2              pass
    2      pass          3nt             double all pass                 
what is the meaning of this double?
This double is asking for Opponent1 lead in the supposted major that dummy should have, in this case asking for lead in as a tentavive to defeat 3nt.
Probable Doubler have KQJ10x and ace as entry in other suit. So the double isn't to lead Clubs!

Doubles in Competitive Auction

 Rule#6- When you overcall and partner denies support at level 2 and opponents go to 3nt and partner then double, this means partner don't have honors in your suit, but have honors in the first suit bided by dummy and want use this lead to make a trick and shift to your suit. 
example7.6
65 82 KJ943 AQ107
AQ6 KJ10843 75 92
AJ5 Q743 K109 862
K8743 5 AQ6 J1092
Opener Vul Overcaller NVul Responder Vul Advancer NVul
       pass 
 1   1   1 pass 
1nt pass  2nt pass
3nt pass pass double and all pass

Lead 8 defeat the contract because Advance make 10 and shift to 9 and declarer let Advancer make the trick but Overcaller cover with 10 and  play Spades again and 7 win the trick and Advance play 2 for declarer A. Declare play 2 round of Clubs and Overcaller discard a . Declarer play more 2 rounds in Clubs and Advancer make the J then play A for down 1. 

Note: if Overcaller lead Hearts Declarer has 2 tricks in Hearts, 4 Tricks in Clubs and can endplay Advance to gain the niteth trick in Diamnds or in Spades or just try Diamonds finesse with success, thus the logic of this double is clear to lead Spades and not lead Hearts because Advance do not support partner suit. So here occurs a very accurate defense!      
Rule#7- When partner overcalls and advancer doesn't support overcaller suit at level 3 but after 3nt double the contract of 3nt, this means Advancer have honors in overcaller suit but no condicions to bid at level 3, so overcaller must lead his on suit. Observe that this double never could be aksing lead in Diamonds.
example7.7
A109 KQJ7 842 532
AJ9 K108652 7 Q43
K872 5 QJ1093 A64
AQ2 75 KJ43 10986
Opener Vul Overcaller NVul Responder Advancer
 1   1   3  pass
3nt pass pass double and all pass
Opener Overcaller Responder Advancer
  1         1             3             pass
 3nt        pass         pass         double*    all pass
* asking for Hearts lead
Lead in 6 defeat 3nt after a accurate defense.
trick01- Q make the trick
trick02- K make the trick
trick03- Overcaller shift to K and win the trick
trick04- Q is played and win the trick
trick05- J is played and A win the trick
trick06- A win the trick
trick07- Q win the trick
trick08- K win the trick
trick09- J win the trick
trick10- A win the trick for down 1
Note- if the lead was K then declarer make A and after play K Advancer make A and shift to Q but declarer have now 9 tricks. thus the double for lead Hearts was fundamental to defeat the contract with the shift to Spades by Overcaller to maintain the communication.
Rule#8 - When overcaller in a major and at end of the bidding reopen 3nt with double this is asking for Advance lead in his shorter unbid minor suit and forbiden Advancer lead in his bided suit, so Advancer must select a possible dubleton minor to lead!
example7.8
A76 Q10982 KJ4 53
A9763 82 Q10 KJ85
A72 KQJ102 984 76
Q2 A KJ104 98653
Opener Vul Overcaller NVul Responder Advancer
 1   1  1nt pass
2nt pass 3nt pass
pass double * all pass  
* shows spades stopper and 8-10 hcp
** asking for lead in a shorter minor
Knowing the convention it was easy for Advancer the lead of 7 and after two rounds of Diamonds declarer play Clubs for down 1.
If Spades is the lead declarer could play Clubs and withdraw Overcaller entry thus with the double finesses in Hearts contract could be make.
Rule#9 - When partner overcalls and Responder bids a major at level 1 and Advancer bids another suit at level 2 if they go to 3nt the Advancer double forbid partner lead in his on suit and in Advancer suit so the lead must be in the first suit bidded by dummy as a way to Advance take the tricks and play Overcaller suit.
example7.9
85 62 KJ1043 AQ9
K1042 AQJ9752 8 72
K1082 Q5 AJ974 63
AK3 4 Q72 J109865
Opener Vul Overcaller NVul Responder Advancer
 1   1   1    2
2nt pass 3nt double *  and all pass
* double is asking for lead Spades the suit bidded by dummy at level 1
 Lead 6 defeat the contract
trick1 Q win the trick
trick2 J win the trick
trick3 A win the trick
trick4 Q win the trick
trick5 A wint the trick for down 1 
Note: If the lead was Q declarer can make the contract finding Q

 Rule#10- When partner overcall and Responder bid a suit at level 2 and Advancer bid also a suit at level 2 and Opener go to 3nt then Advancer double is asking for lead in his suit, not in partner suit.
example7.10
K7 QJ109862 A4 53
AK974 Q2 43 J1085
A65 73 984 KQJ102
982 76 AQJ104 K3
Opener Vul Overcaller NVul Responder Advancer
      pass
 1   1  2 2
2nt pass 3nt double*   all pass
* double is asking for lead and not for lead because the suit bided at level 2 is supposted be a good suit.
trick1 10 win the trick and return K
trick2 A wing the trick and play Clubs finesse
trick3 K win the trick for down 1
Note: If Overcaller leads Q - a solid lead - declarer makes the contract with 4 tricks in Clubs 2 tricks in Hearts 2 tricks in Spades and 1 trick in Diamonds.

 8- SUPPORT DOUBLE AND REDOUBLE
This is a popular convention introduced by Eric Rodwell to clarify after a interference a support made with 3 cards x 4 cards
 Opener Opponent1 Responder Opponent2
  1          pass              1                  1
   ?
 pass    <= denies 3 cards support in Hearts - and 11-15 hcp
 double <= shows 3 cards support in Hearts - undefined strength
   2      <= shows 4 cards support in Hearts - and 11-15 hcp
  2      <= shows 4 cards support in Hearts - and 18-19 hcp GF
  3      <= shows 4 cards support in Hearts - and 16-17 hcp
  4      <= shows distributional hand with 6+4+ and 15+ hcp

Opener Opponent1 Responder Opponent2
  1        pass           1               double
  ?
 pass        <= denies 3 cards support in Spades - and 11-15 hcp
redouble  <= shows 3 cards support in Spades - undefined strength
  2          <= shows 4 cards support in Spades - and 11-15 hcp
  3          <= shows 4 cards support in Hearts - and 16-17 hcp
  4          <= shows distributional hand with 6+4+ and 15+ hcp

Opener Opponent1 Responder Opponent2
  1        pass           1*             1          *Walsh convention        
 pass    <= denies 3 cards support in Diamonds - and 11-15 hcp
double <= shows 3 cards support in Diamonds - undefined strength
 2       <= shows 4 cards support in Diamonds - 11-15 hcp
 2       <= shows 4 cards support in Diamonds - 18-19 hcp
 3       <= shows 4 cards support in Diamonds - 16-17 hcp
 3       <= shows 4 cards support in Diamonds - 15+ hcp singleton

Note = support double do not apply to level 3 unless special agreement and neither after 1nt overcall.

Opener Opponent1 Responder Opponent2
  1        pass            1 suit         1nt
double <= penalty double not a support double - shows 16+ hcp
Opener:  A6 K102 K3 img_site/clubs.gifKQJ1083

9- DOUBLE AND REDOUBLE ROSENKRANZ

Dr. George Rosenkranz, doctor and research, was also a theoretical in
bridge (creator of ROMEX system) introduced the Rosenkranz convention.

 Rule#11: if partner overcalls and the opponent at your right side bids in
level 1 or level 2, if you have a top honor A or K in your partner suit you
say that applying a double and if you just support your pd then you deny
top honor. Of course, your partner after your double must rebid his suit.
The advantage of this convention is in lead, because if your partner has
AQ... and you deny honor with just a support in his suit, he must lead in
another suit! 

examples:
a) Opener   partner    Responder      you
       1img_site/clubs.gif           1img_site/spades.gif             double             ?
if your hand is: img_site/spades.gif K3 img_site/hearts.gif 72 img_site/diamonds.gif J8543 img_site/clubs.gif J1043 bid redouble;
if your hand is: img_site/spades.gif J97 img_site/hearts.gif QJ2 img_site/diamonds.gif KJ7653 img_site/clubs.gif 3 bid 2img_site/spades.gif;

b) Opener  partner    Responder       you
       1img_site/clubs.gif           1img_site/spades.gif             2img_site/hearts.gif                   ?
if your hand is: img_site/spades.gif K3 img_site/hearts.gif 72 img_site/diamonds.gif J8543 img_site/clubs.gif J1043 bid double;
if your hand is: img_site/spades.gif J97 img_site/hearts.gif QJ2 img_site/diamonds.gif KJ7653 img_site/clubs.gif 3 bid 2img_site/spades.gif;

c) Opener  partner   Responder        you
       1img_site/clubs.gif           2img_site/spades.gif          double               ?
if your hand is: img_site/spades.gif K3 img_site/hearts.gif 72 img_site/diamonds.gif J8543 img_site/clubs.gif J1043 bid redouble;
if your hand is: img_site/spades.gif J98 img_site/hearts.gif Q2 img_site/diamonds.gif KJ7653 img_site/clubs.gif 3 bid 3img_site/spades.gif;

d) Opener  partner    Responder      you
       1img_site/hearts.gif           1img_site/spades.gif               2img_site/hearts.gif                ?
if your hand is: img_site/spades.gif J3 img_site/hearts.gif 72 img_site/diamonds.gif AJ543 img_site/clubs.gif KJ103 bid double
to show the other two suits.

Of course if your partner pass after a competitive double
you should consider in change partner!

10-REVISION
a) Opener Opponent1 Responder Opponent2
     1          pass          1nt            2img_site/clubs.gif
   double <= negative shows void in Clubs or 5341img_site/clubs.gif 12-15 hcp
                     if Opener has 4 cards he should bid 2
b) Opener Opponent1 Responder Opponent2
     1          pass          1nt            2
   double <= negative shows void in Diamonds or 5314img_site/clubs.gif 12-15 hcp
                      if Opener has 4 cards he should bid 2

c) Opener Opponent1 Responder Opponent2
     1          pass          1nt            2
   double <= negative shows void in Hearts or 5143img_site/clubs.gif or 5134img_site/clubs.gif
                     and 12-15 hcp
d) Opponent1  You    Opponent2 Partner
     1img_site/clubs.gif             double   2img_site/clubs.gif             double *
* responsive shows 2 suits - deny 5 cards in major - 6-9 hcp
possibles distributions: 4 4 x ximg_site/clubs.gif or 4 x 4+ ximg_site/clubs.gif or x 4 4+ ximg_site/clubs.gif

e) Opponent1  You    Opponent2 Partner
     1              double  2             double *
* responsive shows 2 suits - deny 5 cards in major - 6-9 hcp
possibles distributions: 4 4 x ximg_site/clubs.gif or 4 x x 4img_site/clubs.gif+ or x 4 x 4img_site/clubs.gif+

f) Opener Opponent1 Responder Opponent2
     1img_site/clubs.gif          pass          1             2
   double <= support shows 3 cards in Spades  12-19 hcp

g) Opener Opponent1 Responder Opponent2
     1          pass          1             1
   double <= support shows 3 cards in Hearts   12-19 hcp

 h) Opener Opponent1 Responder Opponent2
     1          pass          2              3img_site/clubs.gif/3/3
   double <= competitive - invitation to 4
                      Responder with a singleton and 8 hcp must bid 4
                     or with 2 sure tricks (AK) must bid 4

i) Opponent1  You    Opponent2 Partner
     1              pass    1nt             pass
    pass          double *
* penalty - asking to partner lead his top card in

j) Opener   opponent1  Responder opponent2
     1           double       redouble    pass 
    pass        1/2img_site/clubs.gif/2  double *     pass
      ? <= Openert should pass - misfit hand
* penalty - all doubles after redouble are penalty but if Opponent2
                  bid a suit then with singleton Opener should bid his
                  second suit or rebid his 6 good cards in his suit.

k) Opponent1 You   Opponent2 Partner
     1              pass   2              3
     4              pass   4nt             pass      All Vul
     5              pass   7              double
     pass           pass   pass
what is your lead with: xx xx xxxx img_site/clubs.gif xxxxx
Answer: partner forbidden lead in his suit with the double, so this is a tipical Lighttner double to ruff. You should lead in your longest suit but
in this bidding it is difficult suppose opponents with 8 cards in Clubs, so you must lead Diamonds that could be a strong and long suit in dummy.
Opponent2 could have: - Kxx AKQJxxx img_site/clubs.gif KQx
     Partner could have: AQJ98765 xx - img_site/clubs.gif xxx
 

That's all folks