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It is clear to me that strong club systems should use the 1D opening to show spades.
When a spade fit exists, it is important to find it, because spades out-rank all other suits. If you open 1NT and miss your heart fit, this is less likely to matter, because the par contract could well be 2S by your opponents. Indeed, you may find you get a good board when your weak NT preempts the opponents out of their spade fit. For this reason, I believe that you should try to avoid opening 1NT with 4 spades, but to freely open it holding 4 hearts and 2-3 spades.
As your opening showing spades already includes balanced hands, but your opening with hearts does not, it is preferable to put hands with 4-4 in the majors into your opening showing spades. Also, assuming that you don't have an opening to show both majors, it is clear to show spades first on all hands with 5+spades and 4+hearts, because this allows you to follow-up with a rebid in hearts. If you show hearts first, you may then want to introduce your spades later, forcing preference to hearts a level higher. Indeed, there is a case for showing spades first even with 4 spades and 5+hearts, intending to bid both suits yourself. In this case, it is clear that you should use 1D to show spades (as opposed to using, say, 1H and 1S both showing spades).
With an unbalanced hand with only 4 hearts, the situation is different; if you pass a natural 1NT opening and miss a 4-4 heart fit, you are unlikely to have missed a good 4♥ contract. If you opened a natural, unbalanced 2m and partner, assuming a misfit, passes, you could well have missed a good 4♥ contract.
So, I think it would be an improvement on current MOSCITO variants to have -
1C = strong
1D = 4+spades
1H = 4+hearts, either unbalanced or 5332
1S = 4+diamonds, either 6D or both minors
1N = 11-14 (or whatever), denies 4 spades or 5 hearts
2C = natural, 6+cards
When holding 4S5+H it would clearly be superior to open 1H in this context, as it promises an unbalanced hand and allows opener to differentiate between having longer hearts and equal or longer spades.
The problem with this is that your (very frequent) 1D opening isn't that well defined. I believe that MOSCITOers generally believe it is right to raise freely to the 2 level with three card support, but when responder is balanced this can easily be a silly contract. Similarly, with four card support, it isn't clear to responder whether to raise/compete to the two- or three-level, and if he raises to only the two-level opener won't know to place him with a fourth trump.
With an unbalanced hand without a 4 card major, natural openings at the two level work well; They preempt against the opponents presumed major fit, and leave partner well placed to further the preempt, knowing that opener either has a six card suit or a bit of shape - (13)(45) pattern. This is especially advantageous when opening in first seat, as you can have the auction at a high level before 4th seat gets his first chance to call.
These points encourage me to use a natural, constructive 2D opening, and remove some hands from the 1D opening into the 1S opening. The downside to this is losing 2D from the preemptive structure, but I think that is a price easily worth paying. Nick Hughes suggests using 1S as both majors, and I think that this works very well, as when partner opens 1D or 1H and you have length in the both majors, you can happily preempt knowing that you aren't missing a better fit in the other one; when you hold length in partner's major and shortness in the other, you can preempt higher against the opponents' known major-suit fit. (FWIW, using this structure I would prefer to open 1NT on 4=3=3=3 patterns, giving responder the guarantee of a little shape for a 1D opening).
Instead, I advocate using 1D to show precisely 4 spades and 1S to show 5+.
[beginning of edit]
When partner has opened 1D, responder will initially assume that he has a flattish hand (he will be balanced or 4(225) approximately 70% of the time). He doesn't feel the need to raise on a flat hand with 3 card support to cater to partner having a suitable hand for playing in spades, but he can still raise on 3 cards when holding an outside singleton. It is much less likely that opener, having promised precisely 4 spades, will wonder whether he should be competing further later; responder is firmly in control of the auction.
When opener has five spades, responder is able to compete higher or preempt further than he would opposite a 4+card opening. There is also no later confusion over whether opener has a canapé opening or not, as he has shown or denied a 5th spade with his first bid. This is very useful both in contested and uncontested auctions.
Are the gains of this method greater than using a 1S opening to show both majors? I believe so. Splitting the balanced hands with four spades between the 1D and 1S openings seems wrong to me, it makes it much harder to judge when partner has a weak NT. My method also allows more balanced hands to be opened - In an uncontested auction there is room for opener to show a minimum or maximum, while in a contested auction responder can usually find an action if he wishes to be in game opposite a maximum. 4432s with 10-15 points and 4333s with 11-15 points can open 1D quite comfortably.
Compared to MOSCITO, I feel that we are better placed in competitive auctions on nearly all hands with a 4+card major (arguably, the exception being hands with 4S5+H). Unlike MOSCITO, our 2C opening can be (13)45, but I think that the loss there is minimal. It's hard to say how the natural 2D opening will compare to the MOSCITO 1S opening showing 4+D. Overall, I think this system leaves partner better placed in competition than any strong club system I have seen.
So, what are the losses? Well, as mentioned before, we've lost the 2D opening from our preemptive structure. Also, starting with 1S rather than 1H on hands with 5+spades pushes us up in uncontested auctions, particularly as 1NT is probably needed for investigating the best part-score.
[End of edit]
So, here we have Gemini - so called due to the twin openings showing spades.
1C - any 16+, or rule of 25 (EBU regulations require this) (10%)
1D - 10-15, precisely 4 spades, any shape (10.5%)
1H - 4+hearts, 0-3 spades, if precisely 4 hearts then will be 1444 or have a longer minor (8.5%)
1S - 5+spades (7.2%)
1N - 12-15, denies 4S or 5H (7%)
2m - 11-15 nat, unbal, denies a 4 card major (1.8% each)
2NT - 5+/5+ minors, fairly offensive when vul
Btw, this opening structure is legal under the ACBL GCC. I don't know whether any sensible continuations are permitted.
Some of my calculations of the frequencies of the openings do not merit the level of precision given above! 22(45) would always be treated as balanced; (24)(25) and 6m322 would open 1NT if particularly suitable, as may the odd (13)(45), with a stiff king and a poor five card suit. 7-4 patterns would be treated as single-suited, indeed there is a case for opening 2m on some hands with 6m4M.
The response structure is not yet finalised, but I am leaning towards -
1D:
1H = natural F1
1S = ART INV+
1N, 2C, 2D = nat NF
2H = 4+spades, inv+
2S = 4 cards, or 3 cards with an outside singleton, weak
1H:
1S = ART, denies 5 spades or 3 hearts, looking for best strain
1N = ART GF
2C = 5+spades
2D = 3+hearts, inv+
2H = weak raise
1S:
1N = NF/F1
2C = ART GF
2D = 5+Hearts
2H = 3+spades, inv+
1N:
Standard stuff, except invitational hands with a 5 card major go through "Stayman"
2m:
Step one ART enquiry, otherwise 2M is natural constructive NF
2D:2NT = hearts, F1
This post has been edited by MickyB: 2007-March-02, 20:06