Three Diamond Checkback

I received this from Greg Morse, gmorse, and have reproduced it almost in its entirety. Mr. Morse cites Hardy's 2/1 as his source for finding this convention.

The Three Diamond Checkback bid is used after Opener has made a strong rebid of 2NT.

It works like this:


Opener is showing 18-20 HCP and a balanced hand. He has denied 4 card support for responder's major but he may have 4 cards in the other major.

If responder has a weak hand (less than 7 HCP) he can use the Wolff relay (3C). If responder has enough for game and is lookig for a major suit fit he bids 3D*. This is completely artificial, even if opener's bid was 1D. It asks opener to describe his major suit holding. Presumably (see later) responder is looking for a major suit game, either 5-3 or 4-4.
Opener's first responsibility is to show his Hearts. The sequences vary as follows:

(a) 3H - Opener has 3 hearts
(i)3NT Wrong answer. Responder has 4H and 4S and was looking for a 4-4 spade fit.

(b) 4S Opener has 4 spades as well as 3 hearts.

(i) 4H Responder has 5 hearts. (and no slam interest presumably)
(ii) 4NT/Cue hearts agreed trump suit. Slam exploration.
(c) 3S- Opener has 4 spades, and only 2 hearts. (With singleton heart he should not rebid 2NT)

(i) 3NT Wrong answer. Responder has 5hearts and was looking for a 5-3 heart game.
(ii) 4S Responder has 4S and 4(or 5) hearts.
(iii) 4NT/Cue Spades agreed, slam exploration etc.

(d) 3NT Opener has only a max of 3 spades and 2 hearts.

(i) 4H Responder has 6+ hearts. He used 3D to find out more about opener's hand.

After 1m-1S;2NT-3D*

(a) Opener
3H - Opener has 4 hearts. (Note 4H needed here where only 3 needed previously)

(i) 3NT Wrong Answer. Responder was looking for 5-3 Spade game.

4S Opener has 3 spades also.

(ii) Responder
4H Responder has 4 hearts. (and presumably 5+ spades since he bid spades first). If Opener has 3 card spades and slam interest here, he might keep bidding.
(iii) 4NT/Cue hearts agreed. Slam exploration.

(b) Opener
3S Opener has 3 spades, but does not have 4 hearts.

(i) 4S Responder must have at least 5 spades to have used the 3D* bid here. with 4-4 in the majors he would bid 1H first.
(ii) 4NT/Cue Spades agreed. Slam exploration.

(c) 3NT Opener does not have 4 hearts or 3 spades.

(i) 4S Responder has 6+ spades. He used 3D to find out more about opener's hand.

As is the case with any bid that forces a relay, responder can use the fact that 3D is forcing to define other artificial auctions.