[mgoetze]

Since I've had it come up twice today... why do 3NT and 2♣-2♦-3NT both show 25-27 balanced?

[georgi]

At the moment the difference between both is the probably occurrence of 5th major.

3NT directly - Strong hand -- 2-5 C; 2-5 D; 2-4 H; 2-4 S; 25-27 HCP
2♣-2♦,3NT - -- 2-5 C; 2-5 D; 2-5 H; 2-5 S; 25-27 HCP

[mgoetze]

So does 2♣-2♦-3NT promise a 5-card major? And if so, how does responder find out which it is?

[cloa513]

A bidding sequence in another thread suggested that GIB considers 3NT direct stronger than 2C,2D,3NT as that GIB reasonably took that 3NT to 6NT and left the other 3NT in.

[barmar]

No, the point ranges are identical. The only difference is that it will never open 3N with a 5-card major, but it will open 2♣ and rebid 3N with it. I have a feeling this is just a historical accident: when they added NT opening with 5-card majors, they simply missed this case.

As for why there are two sequences that show almost the same thing (and were identical before the 5-card major change last year), it looks like it's because Gambling 3N is an option in the system file. So if this convention is enabled, you don't have two ways of showing 25-27 NT. They could have defined 2♣-2♦-3N to have different meanings depending on whether Gambling is enabled (as I think most human players do), but it looks like for simplicity they didn't make it conditional (we'd also then have to adjust 2♣-2♦-4N and so on).

These hands are so rare that it's not very important.

[mgoetze]

barmar, on 2012-February-15, 18:50, said:

it looks like it's because Gambling 3N is an option in the system file.

So... how can we access these options?

[barmar]

If you download GIB to your PC you can construct system files. GIB on BBO always plays its default system.