[Wentys]

The explanation for South's 6♣ bid is "No king (below C)"

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I had this hand (playing Just Declare) which the Robots had bid to 7♣. The 4NT by North was a RKCB ask with Clubs as trumps, followed by 5NT which is explained as "Query Kings". What responses are used after 5NT, and what does the bid explanation "No King (below C)" mean? Did South somehow show that K♠, or did South deny the K♠?

Thanks for any clarification.

[pilowsky]

I think GIB uses SKA - Specific King Ask after 5NT.
So, 4NT is RKCB - 5♣ means 1/4 - which South doesn't have so North 'thinks' South has 4.
5NT asks for Kings so 6♣ means no king apart from the ♣K which is also not true.
7♣ is a sign off.

Maybe smerriman can make sense of it?

[smerriman]

GIB has no way of finding out about the spade king. It has the same logic no matter what trumps is - a bid in any suit that is below 6 trumps shows the king of that suit, and bidding 6 trumps denies such a king. When clubs are trumps, there are no suits below 6♣, and 'no king below clubs' is true 100% of the time.

Why does it bid 5NT if the only possible response is 6♣? It's not; 5NT confirms all keycards so South can bid grand themselves if appropriate (e.g. an undisclosed source of tricks), and GIB is thus forced to bid 5NT to confirm holding all keycards and the queen.

Why does it bid 7♣? Because it's not very good; the free robot will do so with 16HCP. The proper paid robot will simulate and choose between pass and grand depending on what makes more often. But this is why most people don't play 4NT as keycard when trumps are a minor, because there is no room to find out anything.

pilowsky, on 2025-August-20, 05:59, said:

So, 4NT is RKCB - 5♣ means 1/4 - which South doesn't have so North 'thinks' South has 4.

No, 5♣ is 0/3, as it has.