[thorvald]

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What is the Bot bid here?

Spoiler

The Bot doubled

I did orobably misread the explanation as it was nefative, 7- points

I wonder what Pass would show

[helene_t]

That's a fairly normal system. Pass would presumably be a positive with no clear direction, possibly a trap pass.

[pescetom]

We play that meaning of double over 4 level (a positive for us being a K or A), pass is anything else and forcing.
At lower levels double is punishment, as protection against psyches and rubbish.

[LBengtsson]

I have seen X used at the 2 level to show a double negative hand 0-2 HCP - no king or ace hand - but not at the 4 level though I like DavidKok's answer here that lower-level doubles are penalty protection against psyches and garbage by opps.

Imo, I would have thought, given that partner had opened 2♣ probably with a 2 or 3 suited hand not likely containing ♥s in this sequence Pass - 2♣ - 4♥ that X would be best as a penalty here, especially given the vulnerability.

[thorvald]

For those interested

This was my hand

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[pescetom]

thorvald, on 2022-November-04, 10:31, said:

For those interested

This was my hand

Just one data point, but the convention looks ok here: we can't let them play 4♥ vulnerable and we should still make 4♠ easily.
As always it's trickier when they have the spades.