[thorvald]

I am still trying to figure out if there are any rules for what card to lead thru declarer or just later in the play, just like the rules for the opening-lead.

The bot got this East hand

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Now partner leads ♣4, and declarer fails and uses the 9.

Now the bot figures that switching to ♠ is right (as often seen a switch to shortage at dummy)

But what card?

Now change the bidding a bit

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Same lead, and same error by declarer, and GIB again decides to play a ♠ in the two situations

What is interesting that GIB did not play the same ♠

[smerriman]

There aren't any rules, at least not in this situation (but perhaps others like leading from a sequence). It's not bidding related, it just sees 2 and 5 both score identically and chooses one at random.