When responder bid 1 Diamond, the entire context of the auction changes.
At least in the style most common in Brazil (and many other places), the diamond suit is skipped by responder if he is weak (or invitational) and has a 4-card major suit. This includes hands in which diamonds are longer than the major. Responding to 1 Club in this style, you bid your major with, say, KQxx xx QJxxxx x. If your hand has enough to force to game, say, KQxx Ax QJxxx xx, you begin with 1 Diamond. (In North America this is known as the Walsh style).
This has two impacts on the auction:
1. Opener is not required to bid a major with a balanced hand, since if partner has a 4-card major he also has a game-forcing hand, and he will show his 4-card major suit in the subsequent auction. You can rebid 1NT to show a balanced hand in range (12-14 for those who open 1NT with 15-17), with one or even two four-card major suits. This is good for preventing information leakage to the opponents.
1a. The corollary is that when opener does rebid a major, he has an unbalanced hand. At the least, he has a three-suiter (4441). In all other cases he has (at least) 5 clubs and 4 of the bid suit.
2. When opener did bid a major suit after 1 Club - 1 Diamond, responder cannot have 4-card support unless he has enough strength to force to game. That means that a simple (non-forcing) raise of that major shows only 3 cards there, and a hand unsuitable for 1NT (taking into account that opener is unbalanced).
What this all means is that, quite frankly, the standard structure of XYZ is not the best solution for these auctions. But keeping all the auctions under a similar structure has a very big upside of simplifying the memory load of your partnership. I will post some ideas for refinements in these (and other) auctions at the end of this series of articles, but for now let us assume that the XYZ structure is still employed in auctions beginning with 1 Club - 1 Diamond.
With these considerations in mind, let us examine these auctions beginning with 1 Club - 1 Diamond, beginning with the one in which opener rebids spades, since it is most similar to other XYZ auctions we have examined in prior articles.
1 Club - 1 Diamond
1 Spade - ?
Pass: weak hand, 3 spades, expectation that this is the best contract. Usually no stoppers in hearts or an expectation of ruffing tricks, for example, Axx xxx Qxxxx xx.
1NT: weak hand, expects 1NT to be the best contract. A quick change in the prior hand would fit there -- xx Axx Qxxxx xxx
2 Clubs: Forces 2 Diamonds, to play or to begin an invitational auction
2 Diamonds: ART, game forcing. (Another big memory trap here -- practice this auction with your partner if you can!)
2 Hearts - NAT, 4 hearts (and 5+ diamonds), game forcing
2 Spades - NAT, but NF. Hence, it denies four cards in spades. You are giving partner a chance to rebid something with a huge hand (unlike the 1x-1y-1NT auctions, an opener that rebids 1S can have a very strong hand). For example, KJx xxx Axxxx xx.
2NT - forces 3 Clubs, to play there or show a two-suiter. As presented in prior articles.
3 Clubs - Distributional invitation: x Axx Axxxx xxxx. (A partner long in clubs can make plenty of tricks opposite such a hand).
3 Diamonds - It should be a distributional invite, but it has some duplication with the auction 1 Club - 1 Diamond - 1 Spade - 2 Clubs - 2 Diamonds - 3 Diamonds. To keep with the theme that direct jumps are weaker, I suggest you use this as seven cards in diamonds, and the slower sequence then shows 6.
3 Hearts - This very strange bid has no clear use in a natural fashion. I suggest an autosplinter (shortness in hearts) with a game forcing diamond long suit. This will enable you to pass 3NT with clear conscience.
3 Spades - This is not invitational. And it cannot be choice of games once you have found an 8-card suit. My suggestion is to play it as slam interest and very good trumps (at least HHxx). This means that a slower sequence will deny trumps as strong as that.
3NT - To play, 12-14 (it must be quite limited. Remember that opener may be very strong).
There is one other auction that begins 1 Club - 1 Diamond, of course -- when opener rebids 1 Heart. But that situation is so unlike the typical XYZ auction (1 of a minor - 1 Heart - 1 Spade) that using the unchanged XYZ structure means consigning the 1 Spade bid to oblivion. Remember, if responder has 4 spades and bid 1 Diamond originally, he must be strong enough to force to game. It makes no sense for 1 Spade to be natural and GF if we have another cheap GF bid (2 Diamonds), and if responder was prepared to bid 2 Spades over a 1NT rebid. We would be reserving miles of bidding space to a hand that does not need it.
Recommending the use of XYZ under a claim of simplicity and smaller memory load is too much here, even though I place a very big weight on these considerations. Instead, and just for the auction 1 Club - 1 Diamond - 1 Heart, I suggest the following:
1 Club - 1 Diamond
1 Heart - ?
Pass - as in the prior case, a weak hand that believes 1 Heart to be the best contract. Qxx Kxx Qxxxx xx.
1 Spade - Artificial, requesting opener to bid 1NT. You are used to 4th suit forcing here, and so this is a small change. Small but significant. In effect this bid brings you the best of both the 2 Clubs and 2 Diamonds bids in the standard XYZ structure. Responder may have one of two possibilities:
a. Signoff (in notrump or in a minor). Responder will pass 1NT or bid 2 Clubs / 2 Diamonds
b. Any other GF hand (as in standard 4th suit forcing), although without 4 cards in spades.
1NT - Invitational, suggesting notrump as the final strain (stoppers in spades, therefore). This is a major gain of this structure. You will be able to play in 1NT when responder has 10/11 opposite a minimum. Picture K109 xx AQxxx Jxx
2 Clubs - Invitational. Same idea. xx xxx AQxxx Axx. (Remember that opener is unbalanced).
2 Diamonds - Invitational - You get the drift. xx Kx AQJxxx xxx
2 Hearts - Invitational, with nice 3-card support in hearts. xx KJx Axxxx Qxx
2 Spades - Natural, game forcing with 4 spades (and longer diamonds)
2NT - You don't need 2NT here. I don't have any clever suggestions for you.
3 Clubs - Invitational, but with at least 4 clubs.
3 Diamonds - Invitational with long diamonds. Isn't this duplicating with the direct 2 Diamonds bid? Yes, it is. Hence, 3 Diamonds can be something more specific. I suggest 7 diamonds.
You have a great abundance of invitational bids. If you have a game forcing hand, just bid 1 Spade (as you always did, 4th suit forcing), and then bid something above 2 Diamonds when opener obliges by bidding 1NT. 2 Hearts, for instance, shows 4 hearts, and therefore GF strength with longer diamonds.
Next article will explore some aspects of the 1 minor - 1 Heart - 1 Spade - 2 Diamonds auction that makes it different from the 2-way checkback case.