Muddle over RKCB
Please can you tell me how this should be adjudicated?
Only N and S bidding.
N opens 1C and S responds 1H
N bids 4NT and S alerts RKCB and responds 5D
At this point N announces aloud "I have got myself in a muddle" and bids 6C.
Smiles aside, N did get themselves in a muddle and has a void in HEARTS!
N has made an error with the 4NT but the pair do play this and S's 5D response is appropriate for their hand.
Comments
South has Unauthorised Information which he must avoid taking advantage of. Depending on the hands and their further agreements, it may well be that South should be bidding 6H at this point, and if so an adjustment should be considered, as well as a clear explanation to South of his responsibilities when in receipt of UI.
The details of the pair's RKCB agreements here are very important – South mustn't make a call that's suggested over a logical alternative by the unauthorised information, and the RKCB agreements will determine what the logical alternatives are.
The way we play RKCB in my main partnership, there would likely be no logical alternative to Pass – we play that 4NT here asks about keycards for hearts but does not necessarily show a heart fit, and that 6C is a signoff. It is possible that if S has extremely good and long hearts, they would pull to 6H anyway, but would not be expecting more than minimal support from North (North could have chosen to ask in clubs instead, which does have implications for North's hand, but a singleton King of Hearts would be a possible holding). But different pairs play RKCB differently, so depending on the pair's agreements, this could for them be anywhere from an absolute signoff (and thus 6C is passed with any hand), to a shown heart fit (which might potentially make 6C a grand slam try and thus 7H a logical alternative).
Note that North also has some amount of unauthorised information here, because the 4NT bid is not alertable (Blue Book 4B4 – 4NT is never alertable) and yet S alerted it anyway. It isn't clear that the unauthorised information suggests any course of action in particular, though, because North probably didn't mean 4NT as natural.
In my system, 4NT would be RKCB with hearts assumed as trumps for the responses, but not agreed.
6C would therefore be to play.
I suspect this is quite common amongst simpler systems.
We also have a "if you don't understand a bid, pass it" rule.