[lycier]

This is a interesting hand.

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Today I play against Gibs, see 9th round, Gib W inexplicably discards trump ♥4, my result is 4♥+2. So I am gonna think I can make 6♥ contract on a whim. I would better try it again.

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Similarly, see 9th round, Gib W still does a same thing - discarding trump ♥4, even my playing is not best, my result is 6♥=.

[Stephen Tu]

Double dummy it doesn't matter, and presumably GIB is able to see that. If it discards, you can ruff club and lead back to HA and lead club for a coup. Now arguably discard is better in case human opp not able to figure that out, but at this point GIB can't really distinguish between what is an easy play or hard play from a human standpoint. Against decent humans it really didn't cost anything, the takeout double should make the coup rather obvious.

[lycier]

I played against Gibs normally in the first hand, not double dummy.

[smerriman]

Stephen Tu is talking about Gib, not you. Gib defends based on double dummy simulations; all simulations prove you can make all remaining tricks regardless of the card Gib plays, so it doesn't see one as better than another.

[Stephen Tu]

Yeah I know. My point is that at the point in play you are questioning, GIB can see that all plays are equivalent, the hand is essentially face up for everyone at that point. You are always taking all the tricks if you play correctly. So underruffing doesn't cost. It only costs against a bad player who can't see the line. The software isn't really able to distinguish easy plays vs moderately difficult plays vs hard plays for humans. To computer correct line for declarer is trivially easy, so it thinks underruff is equivalent play so it will go ahead and randomly play it since it makes no difference. It can't comprehend that a bad human might cash the high trump in dummy first instead of ruffing club.

It would take a lot more computation to distinguish plays based on possible bad plays from opps. Current is assuming best play from opps.

[jdonn]

Stephen is right. In fact, a human "should" make the rest of the tricks, since I think it can't cost to ruff a club back to your hand, after which a trump to dummy reveals the exact distribution. Obviously a lot of humans would miss that play, but GIB doesn't know that.

Let me edit to say, it is probably better to ruff a club in hand at trick 2 and simply play to ruff all the clubs in your hand and/or cross ruff. But I am talking about what a human should do at the point you found yourself near the end.