How can it be right to keep xx in clubs

[thorvald]

[hv=url=https://www.bridgebase.com/tools/handviewer.html?bbo=y&lin=pn%7Chuman%2CRobot%2CRobot%2CRobot%7Cst%7C%7Cmd%7C2SAK85HJT5DAK2CAJT%2CST76H4DQT963C9875%2CSJ3HAKQ9872DJ87C3%2CSQ942H63D54CKQ642%7Csv%7CB%7Cah%7CBoard%204%7Cmb%7CP%7Cmb%7C1H%7Can%7CMajor%20suit%20opening%20--%205%2B%20%21H%3B%2011-21%20HCP%3B%2012-22%20total%20points%7Cmb%7CP%7Cmb%7C2C%7Can%7CForcing%20two%20over%20one%20--%2013%2B%20HCP%3B%20biddable%20%21C%3B%2014%2B%20total%20points%3B%20forcing%20to%203N%7Cmb%7CP%7Cmb%7C4H%7Can%7C7%2B%20%21H%3B%2011%2B%20HCP%3B%2012-15%20total%20points%7Cmb%7CP%7Cmb%7C4N%7Can%7CBlackwood%20%28H%29%20--%201%2B%20%21H%3B%20biddable%20%21C%3B%2020%2B%20total%20points%7Cmb%7CP%7Cmb%7C5S%7Can%7CTwo%20or%20five%20key%20cards%3B%20queen%20--%207%2B%20%21H%3B%2011%2B%20HCP%3B%20%21HQ%3B%2012-15%20total%20points%7Cmb%7CP%7Cmb%7C7N%7Can%7C1%2B%20%21H%3B%2025%2B%20HCP%3B%20biddable%20%21C%7Cmb%7CP%7Cmb%7CP%7Cmb%7CP%7Cpc%7CDT%7Cpc%7CD8%7Cpc%7CD5%7Cpc%7CDA%7Cpc%7CH5%7Cpc%7CH4%7Cpc%7CHA%7Cpc%7CH6%7Cpc%7CH8%7Cpc%7CH3%7Cpc%7CHJ%7Cpc%7CS6%7Cpc%7CSA%7Cpc%7CS7%7Cpc%7CS3%7Cpc%7CS4%7Cpc%7CSK%7Cpc%7CST%7Cpc%7CSJ%7Cpc%7CS2%7Cpc%7CHT%7Cpc%7CD6%7Cpc%7CHK%7Cpc%7CC2%7Cpc%7CHQ%7Cpc%7CC4%7Cpc%7CCJ%7Cpc%7CC9%7Cpc%7CH9%7Cpc%7CC6%7Cpc%7CS5%7Cpc%7CC8%7Cpc%7CH7%7Cpc%7CD4%7Cpc%7CS8%7Cpc%7CD3%7Cpc%7CH2%7Cpc%7CSQ%7Cpc%7CCT%7Cpc%7CD9%7Cpc%7CDJ%7Cpc%7CS9%7Cpc%7CDK%7Cpc%7CDQ%7Cmc%7C13%7C]399|300[/hv]

 

Try playing this trhu to trick 10. Now remember souths hand is the closed hand, but West is missing ♠9, ♣AKQ and ♦K2-

 

What simulation shows West tha throwing a ♣ can be wrong?

[smerriman]

This one of GIB's most well known play issues, and comes up regularly in the forum.

 

Your 2♣ bid promised 4 clubs, West believes you, and doesn't include this hand in its simulations. It concludes it makes no difference what card it throws.

 

Actually, when I ran GIB and it ran 290 simulations (way more than the BBO robot does), 289/290 times it didn't matter what it played, and on one singular deal it did, thus it played a club. But on BBO, it's highly likely that hand will never come up.

 

Regularly suggested that in end positions GIB could easily deal all possible arrangements and gives ones it thinks are impossible a tiny weighting, just to break ties. But not implemented.

[johnu]

What simulation shows West tha throwing a ♣ can be wrong?

The technical term is a "GIB" simulation. Some will point out that 7NT "guaranteed" 25 HCP. So far, declarer has only played 13 HCP. So in the last 3 cards, South must have 12 HCP so must have all the rest of tricks and whatever West plays is irrevelant.

[smerriman]

The technical term is a "GIB" simulation. Some will point out that 7NT "guaranteed" 25 HCP. So far, declarer has only played 13 HCP. So in the last 3 cards, South must have 12 HCP so must have all the rest of tricks and whatever West plays is irrevelant.

Somewhat surprisingly, it does conclude the slam is going down on 73 of the 290 cases I mentioned above, so that's not actually the case. It puts more emphasis on the 4 clubs than the 25 points.

[thorvald]

Yes, it would be a great improvement to stop simulation in the 4-card ending. It would be possible to calculate all combinations, and then select a discard among the ones where it would matter.

 

On the actual hand the reasoning that south should have 25+ HCP is flawed as soon as North has shown 7+♥ but that is probably to difficult to implement