[jallerton]

1NT=10-12

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IMPS scoring, screens in use.

2♦ was clearly shown on the N/S convention card as "game forcing Stayman" and was described as such by South to West. The auction was as shown above with West declaring 3NT.

North led ♦K, on which South played the 9.
North switched to a spade on which South played the Q.
Declarer now emerged with 12 tricks.

At the end of the hand, West called the TD to record North's "obvious" psyche of FG Stayman.
However, it transpired that:

(i) On the other side of the screen, 2♦was initially described (in writing) as a weak take-out, then corrected to FG Stayman on the next round of the auction when he saw his partner's 2♠ bid. East did not look at the N/S convention card.
(ii) If East had known on the first round of the auction that 2♦ was FG Stayman, he says he would have overcalled 3♣ or 4♣.
(iii) North/South used to play 2♦ as a natural weak take-out over their mini NT, but had recently switched to playing it to be game forcing Stayman.
(iv) Against NT, North/South normally play that the K is a strong lead, asking for unblock or (standard) count.

I have a few questions.

1. In deciding whether to unblock ♦Q at trick one, is South allowed to use the information that they used to play 2♦ as natural here?
2. Should South disclose this information to West? If so, at what point?
3. Suppose that South does unblock ♦Q, beating the contract by 3 tricks. If West claims that he would not have bid 3NT had he known North likely had a natural 2♦ bid, is he entitled to a misinformation adjustment?
4. Suppose that South does not unblock ♦Q, but North guesses to switch to a heart, South then reverts to diamonds, beating the contract by 3 tricks. How do you rule then?

[glen]

Regarding 3, there was no misinformation from South to West, and there is no "misinformation adjustment". There is a lack of information, in that when North passed 2♠, which rules out GF Stayman, South had information that s/he needed to disclose to West. I'm not sure why West did not ask South about North's pass before bidding 3NT.

Regarding 2, North first describes 2♦ as weak takeout (I assume this means takeout to ♦s), and then uses the 2♠ bid to wake up? At this point EW are getting any bad result on the board cancelled. East should call the TD before bidding 3♣.

[gordontd]

glen, on 2012-October-05, 18:56, said:

North first describes 2♦ as weak takeout (I assume this means takeout to ♦s),

Yes, that is what it means.

[gnasher]

glen, on 2012-October-05, 18:56, said:

Regarding 2, North first describes 2♦ as weak takeout (I assume this means takeout to ♦s), and then uses the 2♠ bid to wake up? At this point EW are getting any bad result on the board cancelled.

Why? The 2♠ bid is authorised information, and North has no UI.

Quote

East should call the TD before bidding 3♣.

According to the rules, North should have called the director before correcting his explanation, and East should have called him when North didn't do so. However, I can't see what good this would have done: it appears that the fact weren't in dispute, and it was too late for East to take back his call from the previous round. Calling the director would have the undesirable side-effect of suggesting to South that North had misbid rather than having psyched. Other things being equal, one should try to avoid inflicting a UI problem on an opponent.

[gnasher]

1. Yes. It's information that he possessed before he took his cards out of the board, so it's authorised.
2. Yes. It's "special information conveyed to him through partnership agreement or partnership experience".
The right time to mention it is when he first becomes aware that it may be relevant, which is when North passes 2♠. Assuming this is the first time North has forgotten the change in agreements, we can't reasonably expect South to mention it when he sees the 2♦ bid, because at that point he had no more reason than the opponents to expect North's actual hand.
3. Yes, because with correct information he might well have tried to investigate whether there was a diamond stop. However, it may be subject to the EBU's fielded misbid rules instead. I don't really understand the distinction between misinformation and failure to disclose one's system, but in the EBU this distinction is important because different rectifications are applied.
4. Same as in 3, except that it's more likely to be treated as a fielded misbid.