I will try and document the differences in my non-GF 2/1 system. There are a few variations since we play a weak NT.
jmcw, on 2011-December-05, 23:05, said:
Here are a few sequences that I play in GF 2/1 that MAY have advantages vs a NF approach. Other 2/1 advocates may have other preferred treatments.
1M>>2m>>2M>>2N = 12/14 OR 18/19.
1M>>2m>>2M>>3N = 15/17.
We play
1M>>2m>>2M>>2N as forcing
There are a some of variations here:
1. Our 2M is limited and therefore better defined since stronger hands need to jump. This would seem to give us an advantage on the weaker hands as we are in the some position with more information about opener's hand. There would be a disadvantage on the stronger hands that need to jump and therefore make our 3M rebid less well defined. Some of this disadvantage will be clawed back as the 2/1 players still need to resolve this uncertainty about the range after this start.
2. The difference between 2N and 3N depends not so much on our strength as on our desire for additional information. It would appear there are swings and roundabouts here. Sometimes our 3N will hide information from the opponents that the 2/1 players freely give away. Sometimes opener would rather have been giving some additional information and unsure what to do over 3N.
3. Occasionally with a balanced 12 count we will Pass, yes Pass 2S. It is very occasional. When we judge right obviously this is an advantage and when wrong a disadvantage. With those hands we also have the option of inviting game by raising spades. Again this will be advantageous when we judge to stay out of a bad game.
4. Some of these we handle with
1S>>2m>>3S>>?? at this point responder has more information than the corresponding 2/1 auction to 2S but at the cost of being a level higher. This information maybe helpful or we may regret having used the bidding space.
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1M>>2m>>2N = As above.
1M>>2m>>3N = As above.
As noted we open these hands 1NT in the first case and the 18-19 hands we go through a Mexican 2
♣. The 15-17 hands we would open our major and rebid 2NT. Responder's hand would be less well defined but this is hardly a disadvantage as responder is in control. Responder is at an advantage over your 2/1 auction as we are one-level lower. We do play four-card majors so there is occasionally an unresolved issue about the major suit length.
Given that we might have uninformative auctions like 1NT 3NT or 2
♣ 2
♠; 2NT 3NT with these hands we will at times have an advantage. Occasionally we may miss a good fit by this strategy.
There are other times suited to our methods where we may have an advantage of the 2/1 auctions.
However there are also times where with these hand types we will have disadvantages by having not bid our suits.
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1M>>2m>>3M = A solid suit.
We bid these hands identically but have less information as the 3M rebid also caters to non-solid suits with extra values.
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1M>>2m>>3m = A high honor in the m AND non minimum.
I am not exactly sure what hands you have in here.
With a diamond fit and extra values we can splinter - more information at a small cost to bidding space.
Without a shortage we bid 3NT or 4m. These show extra values at a cost of bidding space. So unless your 3m raise denies a singleton we are at a definite disadvantage here.
Its not clear to me what happens with a minimum and without a high honour. Obviously these hands will be adding a load to one of your lower rebids, presumably 2NT or 2M.
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1M>>2m>>2any>>3M = Good trumps (KQx min) AND a "real" minor suit with 17+.
Same auction but responder delivers less information. We are at a disadvantage.
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1M>>2m>>any>>4M = minimum values good trumps AND NO outside control in the unbids.
Identical auction and information.
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1M>>2m>>any>>2M = Often the start with a slam going hand when a M suit fit exists. Note that neither hand has been limited.
You say often the start with a slam hand but it must also be the start with a game force hand that does not fit a more descriptive bid like the previous one.
Most of these hands we have to bid 3M. This costs us bidding space.
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1M>>2m>>2new>>4th suit = Never needed as a force.
Used as a force.
1M>>2m>>2new>>3m is NF
1M>>2m>>2new>>3new(raise) is NF
Therefore this needs to handle forcing single suiters and forcing raises of opener's second suit as well as other hands with no clear direction.
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I'm not sure how std bidders handle these hand types perhaps they will comment.
To me it appears there are obvious wins and losses for your style of these hands. It is unclear whether the wins out number and out perform the losses.
Some of the losses for our style may be diminished in that there is still two levels to investigate slam and we may well be able to exchange sufficient information in that space to bid to the best contract.
3D = 4th suit