[barmar]

Human dealer, none vul
1♣ 1♦
1♥ 1♠
2♠ 2NT

1♠ is supposedly 4th suit forcing for one round, the explanation said 11+ total points.

The explanation of 2NT was "Invitational to 3NT game -- 4+D, 13-15 HCP". If it has 13-15 HCP, shouldn't it be game forcing? It actually had 12 HCP and 5 ♦.

I think 2NT should just be invitational. What else can it bid with 11 HCP and no fit? With 13 points it can jump to 3NT.

[barmar]

The robot's actual hand was J85 A108 KQ1075 Q8.

[arigreen]

In general, 4th suit forcing is forcing to game. Many people play the auction 1C-1D-1H-1S as an exception. GIB plays this auction as invitational+, but then some of the followups are poorly defined.

We can improve this by providing a clear definition for followups after 1C-1D-1H. Any ideas?

[barmar]

I think most human players use 1C-1D-1H-1S as (ostensibly) natural and 1RF, and a jump to 2S as the artificial game force. With GIB's hand, I would probably bid 2NT instead of 1S, although I admit that the spade stopper is tenuous (and what do you do if the spades are xxx?). Is this a MSC problem?

[junyi_zhu]

arigreen, on Dec 23 2009, 06:21 AM, said:

In general, 4th suit forcing is forcing to game. Many people play the auction 1C-1D-1H-1S as an exception. GIB plays this auction as invitational+, but then some of the followups are poorly defined.

We can improve this by providing a clear definition for followups after 1C-1D-1H. Any ideas?

The simplest way is to play 1S as 4th suit gameforcing, 2NT/3C/3D/3H as invitational,
11-12 total points. Of course, you may have to rebid 2NT without stoppers sometimes,
to solve that problem, you can probably bid 2S to show a invitational hand without spade stopper (after that, 2NT and 3C can be signoffs, otherbids are gf). This treatment is probably the easiest to program IMO.