[calm01]

http://tinyurl.com/6o2vz2t


The simulations that that GIB employed to determine that 4S is better than 3NT must be somewhat warped.

What is going on in the program?

Surely it is possible to trace its path to this unusual decision.

[babalu1997]

calm01, on 2011-December-01, 19:59, said:

http://tinyurl.com/6o2vz2t


The simulations that that GIB employed to determine that 4S is better than 3NT must be somewhat warped.

What is going on in the program?

Surely it is possible to trace its path to this unusual decision.

the bot completed his raise.
after 1nt force, your rebid is 3 clubs or 2nt for some, then he bids 3 spades(lowest spade bid) showing 2 trumps giving captaincy back to you, ie choose 3nt or 4 spades.

he completed his bergen raise that is all

[barmar]

Here's what's going on with this.

The correct rebid with the South hand is 2NT, which shows a hand in between a 1NT and 2NT opener. If you do that, GIB would have raised to 3NT. The 3NT rebid shows a hand strong enough to open 2NT, but you chose to open in your major instead (GIB used to NOT open 1NT or 2NT with 5-card majors, and this rebid is what it used in those cases).

GIB has a rule that says that if it has enough to invite slam in a suit, but not enough to invite 6NT, it rebids 4 of the major over this 3NT bid, even if this means playing in a Moysian. I guess the theory is that you may still be able to get an extra trick by playing in trumps. So even though it will bid this with only 2-card support, we still claim that it "shows" 3, because there's no way to distinguish them and we don't want to discourage partner. The comments in the bidding database admit this:

; a Moysian perhaps, but partner will assume an 8-card fit if possible
; partner makes a lot of mistakes after this rule, but fixing it has no impact

So whoever wrote this rule clearly thought this was the "best lie".

[Bbradley62]

barmar, on 2011-December-05, 18:58, said:

The correct rebid with the South hand is 2NT, which shows a hand in between a 1NT and 2NT opener... The 3NT rebid shows a hand strong enough to open 2NT, but you chose to open in your major instead...

Maybe the description of the 3NT rebid could be changed from "19-21 HCP" to "20-21 HCP" to make this more clear?
Edit: OP, with 19HCP, had no real way to know he was supposed to show "18-19", not "19-21".

barmar, on 2011-December-05, 18:58, said:

GIB has a rule that says that if it has enough to invite slam in a suit, but not enough to invite 6NT, it rebids 4 of the major over this 3NT bid...

But, it would do the same thing with a hand with 3 spades and no interest at all in slam?

This post has been edited by Bbradley62: 2011-December-05, 19:31

[barmar]

Bbradley62, on 2011-December-05, 19:28, said:

But, it would do the same thing with a hand with 3 spades and no interest at all in slam?

Most hands with 3 spades would have bid 2♠ rather than 1NT on the first round. But there are some minimum hands with 3 card support that start with 1NT. The book bid in this case is to pass 3NT, but about half the time simulations tell it to bid 4♠.

Since we now allow opening 2NT with a 5-card major, this situation shouldn't really come up.