[BLML] The Monty Hall trap

Eric Landau ehaa at starpower.net
Fri Dec 10 22:51:26 CET 2010

On Dec 10, 2010, at 4:02 PM, Thomas Dehn wrote:

> Eric Landau <ehaa at starpower.net> wrote:
>> On Dec 10, 2010, at 1:26 PM, Thomas Dehn wrote:
>>> Eric Landau <ehaa at starpower.net> wrote:
>>>> Regardless of any UI considerations, it can't possibly be an LA for
>>>> West to pass short of game holding a 16-count opposite a partner  
>>>> who
>>>> has opened the bidding.  When his partner passes what he thought  
>>>> was
>>>> a non-descriptive game-forcing relay, he is allowed to "know"  
>>>> that he
>>>> is having a misunderstanding without having "used" any UI.
>>> Maybe partner psyched 1D?
>> Maybe he did, but how can that possibly matter?  If it were
>> considered "logical" to take the possibility of a psych (which would
>> be of unknown character, by definition, and thus could "logically"
>> show anything at all) into account in selecting one's call, then
>> literally any legal call becomes a "logical alternative" to a
>> systemic call suggested by UI.
> Partner has passed 2D which West thought is a forcing relay.
> One of the logical alternative is that this pass wakes
> up West and West then remembers that 2D actually was not forcing.
> This LA is suggested by the UI.

I don't understand this.  A "logical alternative action" [L16B1(b)]  
("LA") is a "call or play".  "Waking up" by itself is not a logical  
alternative action.  Partner's pass of 2D might well suggest that 2D  
was actually not forcing (as it did here), but doesn't change the  
fact that West has a game force and knows it, even though he is now  
aware that he accidentally made a non-forcing bid.  It would be  
improper, for example, for him to leap to a game in lieu of making a  
more descriptive call, knowing that his partner didn't take 2D as a  
game force (and so might pass the LA), but nothing like that has  
occurred here.

> The question is whether there are other LAs.
> For that, one has to consider what West might conclude
> from the AI that partner passed 2D.
> Consider the following auction:
> Ali       NORTH     Hills     SOUTH
> ---       Pass      1D(1)     Pass
> 1H(2)     Pass      2C(3)     Pass
> 2D(4)     Pass      Pass      ?
> (1) 10-14 hcp, unbalanced with 2 or 3 suits, usually
> denies a 5-card major (exception, could be 5/5 in
> both majors), may or may not hold either or both 4-card
> majors, could hold as few as zero diamonds.
> (2) Two-way bid.  Either less than game-forcing with a
> heart suit (promising a minimum of 5 or 6 hcp), or the
> first step in an artificial game force relay.
> (3) Shows exactly 4 diamonds, and at least 5 clubs.
> (4) Alerted by East as artificial game force relay.
> What conclusions might West draw from this?

Whatever he likes.  He certainly can't be UI-constrained just because  
partner confirmed his a priori understanding of his own bid.  He can  
play partner to have psyched with any hand he can imagine if he wants  
to, and bid anything he wants, from pass to 7NT, accordingly.  But we  
can't just turn that around and say that if partner had overturned  
his understanding of 2D instead of confirming it, he must select the  
least suggested of his uncontrained alternatives, taking the worst  
result that would have followed from calling anything from pass to 7NT.

Eric Landau
1107 Dale Drive
Silver Spring MD 20910
ehaa at starpower.net

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