aguahombre, on 2012-September-21, 09:38, said:
How do we know, when it was 4th chair's turn to act, that he was calling attention to an invalid auction? Opener didn't do anything to indicate he didn't want to bid 1♠ [...]
Yes he did, he passed. If you think the 1♠ is part of the auction then the auction is invalid because North has made too many calls.