Problem 25. Black to Play 5-1
White - Pips 157
Black - Pips 141
Unlimited game, no Jacoby, no beavers
XGID=--a-AAEbD---bBa-abbbb-B---:1:1:1:51:0:0:0:0:10
To find the best play here, one truly needs to “open one’s mind.”
When I showed this position to a friend who holds a Grandmaster Class 3 title (awarded by the
Backgammon Masters Awarding Body (BMAB)), his immediate reaction was to say that he often blunders in this sort of position. That made me feel a little better, as I failed to even consider the best play. The top play is
the one Karol Szczerek found, breaking the anchor, and hitting outside!
At first, that looks a little crazy. Hitting gives up the only asset Black has managed to acquire thus far. White already has a direct shot at the two blots in Black’s board. Hitting him gives him another. After Black hits, White will hit one of the blots in Black’s board with almost any 2, 3, 4, or 5! The only rolls that miss are 66, 63, 62, and 61.
A little reflection, however, is all it takes to convince yourself that hitting is best. The key is the 16pt. As things stand, White has a double shot to make it. If White covers, Black will be primed behind a five-point block, and the game will be just about over.
Hitting mixes things up. Often Black will be forced into hitting contest. Frequently, Black will be able to advance his anchor after being hit. Other times, he may land in a backgame. And there is always the chance that White will throw a 6 from the bar. As Karol pointed out, any of these alternatives gives Black more winning opportunities than passively allowing White to complete his block.
5k XG2 Rollout – Unlimited game, no Jacoby, no beavers
Code:
XGID=--a-AAEbD---bBa-abbbb-B---:1:1:1:51:0:0:0:0:10
X:Player 1 O:Player 2
Score is X:0 O:0. Unlimited Game
Pip count X: 141 O: 157 X-O: 0-0
Cube: 2, X own cube
X to play 51
1. Rollout¹ 22/16* eq:-0.315
Player: 34.44% (G:10.18% B:0.46%)
Opponent: 65.56% (G:22.60% B:1.65%)
Confidence: ±0.006 (-0.321..-0.310) - [100.0%]
2. Rollout¹ 8/3 6/5 eq:-0.390 (-0.075)
Player: 29.46% (G:9.13% B:0.38%)
Opponent: 70.54% (G:16.64% B:0.70%)
Confidence: ±0.006 (-0.396..-0.384) - [0.0%]
3. Rollout¹ 6/5 6/1 eq:-0.404 (-0.088)
Player: 28.76% (G:8.57% B:0.23%)
Opponent: 71.24% (G:15.96% B:0.62%)
Confidence: ±0.005 (-0.409..-0.398) - [0.0%]
4. Rollout¹ 8/3 4/3 eq:-0.422 (-0.107)
Player: 28.19% (G:7.89% B:0.25%)
Opponent: 71.81% (G:15.54% B:0.61%)
Confidence: ±0.005 (-0.427..-0.417) - [0.0%]
5. Rollout¹ 6/1 5/4 eq:-0.427 (-0.112)
Player: 28.29% (G:7.93% B:0.19%)
Opponent: 71.71% (G:16.02% B:0.59%)
Confidence: ±0.005 (-0.432..-0.422) - [0.0%]
¹ 5184 Games rolled with Variance Reduction.
Dice Seed: 24097225
Moves: 3-ply, cube decisions: XG Roller
Rollout by Taper_Mike
2015-May-08
eXtreme Gammon Version: 2.10.199.2658
61P-65D-41$-42U-11E-32$-52S-54$-C-61U-51-n-do.xgp
n[H A75 I88 P107 i112] "<=5
n[H A80 I87 P105 i111] "&e
The real Fatboy,
Eric Peterson, asked whether slotting the 4pt was the best way to play 54 on roll 8. To see why it is, consider how to play the 5. If you don’t play 13/8, then you have to play 8/3, slotting the 3pt. But if you slot the 3pt with the 5, then the 4 has to come down from the midpoint. Otherwise, you are playing 8/4 8/3, leaving three inside blots. Two down from the midpoint is no option either. That would sacrifice the midpoint. The choice, therefore, is between 13/4 and 13/9 8/3. In this light, slotting the 4pt beats slotting the 3pt on two counts. First, it minimizes blot count at a time when a hitting war is about to erupt. Second, it slots the better point. An XGR++ eval has 13/4 on top by 13 millipoints (i.e., 0.013).
In the practice game where this position arose, I took the tutor’s advice, and made the hit. The bot promptly rolled 62, missing the shots, whereupon I luckboxed into a 21, making both my 5pt and 4pt.
You gotta love this game!
Mike
Last edited by Taper_Mike; 05-11-2015 at 02:01 PM.