AI or UI - missed call.
A player bids 2 Clubs - strong game force. Unfortunately they don't notice that RHO has opened with 1 Club - and are mildly surprised when partner alerts and explains as showing the majors.
Now obviously there is plenty of UI going around (possibly both players) - but can the player use the fact that the opening bid was 1 Club, given that they only seem to know this call was made due to partner's unexpected explanation. The law seems to disallow this since the auction is not AI if it is affected by UI from another source) (16A1(a)).
(At the table 2C was passed out going 6 off - at another table the 1 Club bid was overcalled with 2 Diamonds which was explained as weak (with 21 points!) by their partner (it caused our partnership to overbid to 4 spades partly on the supposition that any finesses would work!)). That I accepted of course as it was partnership understanding!
Comments
We have grappled before with the issue of whether your own bidding is AI to you or whether it is affected by UI from another source. For example, you intend to open 1S but when you bid and partner announces "12-14" you inspect your call and find it is 1NT (meanwhile partner has called and it is too late to change your 1S/1NT bid).
The previous discussion did not reach as consensus and I fear the OP's questions is similarly unclear.
I think there is some information which is blatantly available (the bidding cards during the auction, cards played to the current trick) such that it should be considered authorised even if the player has been prompted by UI to access the information (by looking). But this is not what the law says.
Yes, it does seem to me that it would be inconsistent to say that we can use an extraneous action, such as an alert, to identify a mistaken call if we are going to ask to correct it but not if we are not going to ask, or are too late to ask. However, Robin is correct that this is not what Law 16A1 says.
Taking the situation to its conclusion this does give a little bit of a problem with the "guidance" at White Book 8.16.10. How does one decide whether unauthorised information is used if every (or even 2+ ) RHO's open 1club with that hand? After all the section does say "no one else would".
Admittedly there is another "fish to fry" if the partner makes a bid rather than pass. Given that they passed I suppose there are two people looking for new partners.
CMOT
Law 16A1a says that information that "derives from the legal calls and plays of the current board" (including, I expect, the legal calls and plays themselves) is authorised information if it "is unaffected by unauthorized information from another source". This implies to me that, according to the letter of the Laws, the opponents' calls can actually become UI to you if you only notice them as a consequence of UI from partner (likewise, your own). I'm not convinced that this Law is good for the game, but it seems to me to be fairly conclusive.
It seems to be surprisingly easy to become mistaken about what calls have been made in the auction so far (especially on BBO, which prevents the calls so far in table form and it takes a little thought to work out which table heading matches which player), although I've seen it in real life too. Competitive auctions involving 1NT calls seem to be the most frequent offender (possibly because the situation often comes to light very quickly as calls in such auctions are often artificial and typically vary in meaning radically based on the details of the earlier auction).
The problem is to determine what other players would do in the same state of mind as the player at the table - without the unauthorised prompting them to re-read the auction. If the auction had continued, there would be actions which "no one else would" take if they knew what the auction was - but we have to determine if there are actions which players with an incomplete/confused view of the auction would take. (This situation is almost impossible to poll).
We could imagine that there could be unauthorised information affecting the play. East opens 1C, and South bids 2C intended as an opening bid, and this is passed out. West leads, dummy goes down, bidding cards are picked up, and South asks dummy why they passed, North answers "East opened 1C, and we agreed that 2C overcalls were natural". Now South has UI that was available to him by asking for a review of the auction, but the 1C opening bid is not now blatantly obvious. South will have alternative lines of play, and the unauthorised information suggest playing East for opening values. The alternative lines are ones that players ignorant of the 1C bid might play.
It is not clear how we poll this case
I'm assuming here that by mistaken call Gordon means unintended call (if not please ignore the rest of this post).
I have no problem with this distinction. The purpose of 25A (Unintended call) is to allow correction where there is no possibility of UI because the change of call eliminates it. If the call is not changed and unintended caller is alerted to the fact by partner's announcement / alert / explanation (as opposed to on their own cognisance) then there is UI.
I would also have no problem banning the 2C bidder from knowing about the 1C bid if he is alerted to it by partner (Robin's South asks dummy why they passed, North answers "East opened 1C, and we agreed that 2C overcalls were natural"). Declarer is unwise to ask and Dummy most definitely should not respond.