Hi all,


XGID=-BAABDB-A-A-aa--bb-cbAbb--:0:0:1:53:0:0:3:0:10


What's your play here? Obv, most important, why?

While looking at this problem, I asked myself if I hit and white fans what is the cube action for black? I was pretty surprised by the answer. Can anyone explain it?


XGID=aBAABDB-A-A-aA--bb-cb-bb--:0:0:1:00:0:0:3:0:10

Obviously black has decent gammon chances here and a solid chance to win the game. Is he too good to double or should he cash here? If you think he should cash here, what are you doing to figure out your equity advantage?

Let's take the last question first. After 21/13* and flunk, it's double-pass in a money game with a centered cube, because of the Jacoby Rule. In a match with no score considerations, it looks too good to me. Black is miles ahead in the race, he's guaranteed to cover one blot and will sometimes cover both. Even if he never picks up the second checker, White needs 11 crossovers to bear off a checker, so Black's gammon chances are pretty good. I would play on.

Now the original question. Hitting looks right to me and I don't think it's close. White on roll then has 20 hits and 16 flunks. Black wins all 16 flunks by cashing (I'm assuming this is a money game). Black also wins a couple of the 20 games where he gets hit, mostly the games where he reenters and hits back somewhere. Since Black has 5 blots spread around, White needs to double before rolling to activate gammons. Black has a trivial take.

If Black stays put and just makes his board with 8/3 5/2, he's a significant underdog. White has nine killer numbers that close the 4-point (52, 42, 54, 55, 44, and 22) plus 11 to switch, plus a whole bunch of pick and pass numbers. With Black way ahead in the race, I'll make White something like a 2-1 favorite here, with relatively low volatility. White wins almost no gammons in this variation, so doubling is probably a mistake.

What makes the problem especially interesting is that it looks like an example of a rare breed -- positions where making the right play gets you doubled, while the wrong play holds off the cube. Cute stuff.

Nice analysis, Bill. I had the cube actions right, but struggled with the checker play, which I thought was close.

For future reference, the last three fields of an XGID allow you to check whether a position is for money. Actually, you need only the 3rd-to-last and 2nd-to-last fields. Here are the final three fields of the original position: 3:0:10.

10 = Maximum number of cube turns allowed
0 = Match length (zero for cash games)
3 = Jacoby/Crawford field (depends on Match Length)

Money Games
When the match length is 0, then the Jacoby/Crawford field records two things: 1. whether the Jacoby Rule is in use, and 2. whether beavers are allowed. There are four possible combinations:

0 = Jacoby: No, Beavers: No
1 = Jacoby: Yes, Beavers: No
2 = Jacoby: No, Beavers: Yes
3 = Jacoby: Yes, Beavers: Yes

Match Play
The Jacoby/Crawford field is 1 during the Crawford game, and 0 at all other times.

In the original position, the 3 tells you that this is a money game with Jacoby and beavers. Of course, some posters will include the XGID from a match file, but then pose a problem as if for money. Making it clear what your assumptions are can help avoid confusion later.

Mike