Checkback Stayman, NMF and Crowhurst
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Checkback Stayman, New Minor Forcing and Crowhurst

  I was asked to clarify the differences between these three conventions.  
a) 1 - 1 - 2NT - 3
  I have stated in the new-sheets that 3 here is Checkback Stayman (CBS), and so it is. As I have often said, the 2NT rebid does not deny a 4 card major and opener may have 4 's and/or 4 's for this sequence and the best way for responder to find the major suit fit (if there is one) is to use 3 as Checkback Stayman. Regardless of whether the opening bid was 1 or 1.  
b) 1 - 1 - 1NT - 2
  But this sequence is different. Unless you play Walsh (and as far as I know only Clive and Lewis in our club have even heard of it) then opener's 1NT rebid denies a 4 card major and so the 2 bid is to play.  
  But there is a (small) twist. There is a convention called Crowhurst that uses an artificial bid of 2 after a 1NT rebid. But Crowhurst 2 is not used primarily to find out about major suit fits (although the responses do often say something about opener's majors). Anyway, the Crowhurst 2 convention was invented because Eric Crowhurst does not like to open 1NT with a weak doubleton. So if he has a hand within his 1NT range with a weak doubleton he will open 1 of a suit and then rebid 1NT if his partner bids his doubleton. Thus his 1NT rebid has a very wide range (12-17 if you play a strong NT system). Obviously responder sometimes needs to know how many points opener actually has and so 2 asks. In my opinion it's all nonsense and I have no problem simply opening 1NT with a weak doubleton.  
c) 1 - 1 - 1NT - 2
  And here we see just one problem with the Crowhurst 2 convention. 2 here is traditionally Checkback Stayman (or NMF), asking opener if he has 4 's and/or 3 's. If you play Crowhurst then opener also has to give his point count and responder is not promising either 5 's or 4 's. The responses are simply too complicated for a simple soul like me.  
d) 1 - 1 - 1NT - 2
e) 1 - 1 - 1NT - 2
  Finally, let's look at Checkback Stayman vs. New Minor Forcing (NMF). You are responder and have a decent (let's say game invitational) hand with 5 's after partner opens 1 . So you bid 1 and opener rebids 1NT. 2 by you now would be a weak bid and so you need a conventional bid to find out if partner has 3 's. If your partnership plays Checkback Stayman then this bid is 2 , regardless of whether partner opened 1 or not, so (d). If you play NMF then the asking bid is two of the other minor, so (e).  
  Which is best? I prefer Checkback Stayman as there is then more room in the responses to be specific about the majors and give strength information. Using 2 to ask as in sequence (e) does not give opener enough room to be specific.  
  But, for some strange reason, NMF seems to be the more popular of the two these days.  
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