Problem of the Week #118: September 9


Black on roll.




Black to play 4-3 in these situations:

(a) Cash game, center cube.

(b) Tournament match, center cube, Black trails 6-12 to 15.


Note: All ‘cash game’ problems assume the Jacoby Rule is in effect. That is, you can’t win a gammon unless the cube has been turned.

Just rolled this out for money not a week ago

edit: sorry, I lied. It was two weeks ago.

In this position, Black can play defense, making the 20 point, or he can play offense, by making his 5 point.

The argument for defense is twofold:

1. It is harder, in general, to make a good defensive anchor than it is to improve offensive structure. In Problem #118, for instance, Black’s builder on the 9 point gives him many good rolls to improve his forward block on the next turn. It is only when he rolls 43, however, that Black can make the 20 point.
   
   
2. If Black passes up this opportunity for the 20 point, he may not get another chance. On his turn, White will have about a 25% chance to make the point himself if Black does not grab it first.

In the cash game of part (a), this fine roll should be used to make the anchor. At the match score given in part (b), however, Black is anxious to win a gammon. Without doing all the match-equity calculations, let’s just state that Black should make the “gammon-go” play. White’s rear checkers are split, and Black should try to prime them, or blitz them, as the dice may dictate.

My solution in Part (a): 24/20, 23/20
My solution in Part (b): 9/5, 8/5

For the Record
I am so often wrong that I like to post my record in these messages. It's kind of a truth-in-advertising thing. Grunch: I have been answering these problems without the use of a bot, and before checking the excellent solutions of others, since Problem 28. My record at this writing is 49%.

In general, offense comes first in the beginning. But the golden point isn't alone a defensive anchor, but an asset, which allows bold play in the future. The possibilities aren't so much to grab it. There is the number, go for it.

If we make the 5 point, our 6 point remains stacked, it is difficult to unload it in the future with no builders in range and the stripped 8 point.

Because the 20 point is such a key point and the structure after making the five point is just to ugly, i would grab it in both cases.

20. Up with a capital U in both, a) and b).

Grunch.

Make the 20 in both cases I think. Getting the five is a real ugly move.

a) 24/20 23/20

b) 9/5 8/5 as it increases your chances of a gammon.

13/9 24/22 for both.

There is something on bgonline too, but not for AtS. Checked today. I think you can't know it OtB, what is right. You need reference positions.

You say "neither" to the offer of "either."

Truly, you are your own man.

A- make the 20, nice defensive anchor

B- gammon go, make the five

It's the chess player in me. I like the pretty looking set ups. And I mean 24/21 of course. 9pt less valueable but rest of position looks lots better.
Also don't know why it would be different at this score and cash. But I'm not too smart about match equities and such.

The play is different ATS because you are trailing the leader and you need to make up ground in the match. it's called gammon go and there's a lot of info on bgonline. Basically it means you try to make the most gammonish plays which in this case means making a home board point over an anchor.

btw, not arguing with your play, but this score is not even close to real gammon-go. In a money game you need to win twice the amount of gammons to compensate for your extra loses. Or you can say your gammon "price" is 0.5.

At real gammon-go you only need to win as many extra gammons as your extra loses, or in this case your gammon price is 1.

At this score our gammon price on a 2-cube (because if we make the five point we're likely doubling soon) is higher than for money, but I think it's not nearly as high as you might assume.


edit: I should also mention, that another feature of true gammon-go is that gammon losses are meaningless. Here they don't really hurt that much, but they do cost a little.

I've started to make getting my back checkers into good positions as soon as I get a reasonable chance a priority in most of my games and the results have been very positive, especially if I can make my opponent's five point or bar. I have not found that spending a move or two getting an advanced anchor or trying for opponents bar heavily affects my ability to build a prime. Also, owning your opponents five point can give you shots when your opponent is trying to bring his checkers home later in the game. I say 24/20 23/20 both games, keeping an eye on the cube should the chance occur.

In (b), I would make my own 5-pt. You need offense and some lucky gammons.

In (a), that is tougher. You have the two 5-pts. To a lesser extent, some could be tempted to play something like 23/20 13/9. In a vacuum, some say that the golden point is a tad superior to the offensive 5-pt. Even if my heart says go for the offense, I'll risk the anchor.


(a) 24/20 23/20
(b) 9/5 8/5

24/21 13/9 probably is better than 23/20 13/9, since you don't really need to come under the gun.