Jacoby 2NT
 
 This old convention was created by Oswald Jacoby (1902-1984) Sidney Lenz's partner in the initial FOUR ACES team. Jacoby was selected by Lenz to be his partner in the famous match Culbertson-Lenz in 1931. Jacoby made many systems innovation as the Transfer for major after 1nt open.
 
 This convention receive modifications and now is a standard with the follow rules:
 
 Rule#1: 2nt Jacoby is used by Responder after a open in a major in first or second position and shows 12-16 hcp with 4+ cards support denying singleton and asking if Opener have a singleton/void to be bided at level 3.
  
 The responses after 2nt are:
  Opener    Responder
      1♥       2ST
       ?
 3♠/3♣/3♦    => shows singleton or void in the suit bided;
      3♥        => strong hand 17-20 hcp - Responder should cuebid
      3ST      => balanced hand with 15-16 hcp
      4♣        => 5♥-5♣ with 2 top honors (AK/AQ/KQ) in Clubs - 14-16 hcp
      4♦        => 5♥-5♦ with 2 top honors in Diamonds - 14-16 hcp.
      4♥        => deny singleton/void shows minimum 12-14 hcp
 
 Opener      Responder
      1♠          2ST
       ?
 3♥/3♣/3♦ = > shows singleton or void in the suit bided;
      3♠        => strong hand 17-20 hcp - Responder should cuebid
     3ST       => balanced hand with 15-16 hcp
      4♣        => 5♠-5♣ with 2 top honors in Clubs - 14-16 hcp
      4♦        => 5♠-5♦ with 2 top honors in Diamonds -14-16 hcp
      4♣        => 5♠-5♥ with 2 top honors in Clubs - 14-16 hcp
      4♠        => deny singleton/void shows minimum 12-14 hcp
 
 Rule#2:- After Opener bid his singleton Responder show extra values bidding other suit, or jump to game with minimum 12-14 hcp.
 
 Rule#3: If Opener have chance for rebid his singleton that shows void and the bid of another suit shows Opener's extra values.
 
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 Another version for Jacoby 2nt is:
 Rule#4: If your hand is minimum bid 3♣,
 Opener Responder
   1♠        2nt <= Jacoby 4♠+ cards support 12-16 hcp
   3♣ <= any minimum hand 12-14 hcp - can have singleton
               4♠ <= not interesting if you have singleton
  pass
 ===================================================
Rule#5: If you have 15+ hcp explain your hand
 Opener Responder <= Convention Jacoby 2nt for Spades
   1♠        2nt <= Jacoby 4♠+ cards support 12-16 hcp
   3♣ <= any minimum hand 12-14 hcp - may have singleton
                3♦ <= Do you have singleton?
                      ?  Opener bids:
                     3♥ <= singleton ♥
                     3♠ <= singleton ♦
                     3nt <= singleton ♣
                     4♣ <= no singleton but  A♣
                     4♦ <= no singleton but  A♦
                     4♥ <= no singleton but  A♥
                     4♠ <= no singleton and no cuebid
                     Now Responder decide what to do
 ===================================================
 Opener Responder
   1♠        2nt <= Jacoby 4♠+ cards support 12-16 hcp
    ?
   3♦ <= good hand and singleton in ♦
   3♥ <= good hand and singleton in ♥
   3♠ <= good hand 18-19 hcp distribution 5332
  3nt <= good hand and singleton in ♣
   4♣ <= good hand 5♠-5♣ (2 top honors) 15+ hcp
   4♦ <= good hand 5♠-5♦ (2 top honors) 15+ hcp
   4♥ <= good hand 5♠-5♥ (2 top honors) 15+ hcp
   4♠ <= 6♠ cards with no singleton 15+ hcp
  Now Responder decide what to do
 
 **************************************************************
 Opener Responder
   1♥        2nt <= Jacoby 4♥+ cards support 12-16 hcp
   3♣ <= any minimum hand 12-14 hcp - may have singleton
                4♥  <= not interest if you have singleton    
  pass
 ===================================================
 Opener Responder <= Convention Jacoby 2nt for Hearts
   1♥        2nt <= Jacoby 4♥+ cards support 12-16 hcp
   3♣ <= any minimum hand 12-14 hcp - may have singleton
                3♦ <= Do you have singleton?
                      ?  <= Opener bids
                     3♥<= singleton ♦
                     3♠ <= singleton ♠
                    3nt <= singleton ♣
                     4♣ <= no singleton but A♣
                     4♦ <= no singleton but A♦
                     4♥ >= no singleton
     Now Responder decides what to do 
 
 ===================================================
 Opener Responder
   1♥        2nt <= Jacoby 4♥+ cards support 12-16 hcp
   ?
   3♦ <= good hand and singleton in ♦
   3♥ <= good hand 18-19 hcp - 5332
   3♠ <= good hand and singleton in ♠
  3nt <= good hand 15+ hcp and singleton in ♣
   4♣ <= good hand 5♥-5♣ (2 top honors) 15+ hcp
   4♦ <= good hand 5♥-5♦ (2 top honors) 15+ hcp
   4♥ <= 6♥ cards with no singleton 15+ hcp
 And now Responder decide what to.
 
  Thus, Jacoby 2nt convention may have other versions and so it is necessarily make agreements with your partner to select one version of Jacoby 2nt convention.

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