What is AI?
The bidding goes
1NT - P - P - 2C - P.
At this point the partner of the 2C bidder alerts and explains it as being 23 points plus. (the alert might have happened before the 2nd pass, that was the situation when I was called) From partner's reaction he looks round, sees the opening 1NT bid and then calls me to say that he has given a misexplanation. He then advises opponents (correctly) that it is Landy and I offer the NT bidder the opportunity to change their call given the correct explanation (they could, for instance have wanted to double the 2C call to be lead directing had they held good values).
I let matters rest at that point, but should I? i.e. have the pair start on a strong 2C sequence?