hit or build problem; from an online test of Bill Robertie's

[Dungeoneer]

From http://www.bkgm.com/articles/Robertie/AnnotatedGame-TestYourBackgammon/index.html

Move 6: South(Magriel) leading 2-away/5-away to play 6-2 (pls see 1st attachment)

Spoiler

Robertie favors down and slotting the bar-point, gnubg (2nd attachment) favors hitting. I think Bill Robertie was right despite gnubg's eval

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*spoiler warning*: the 2nd pic is gnubg's eval

EDIT:  GNUbg ID:
sOfEAQxwJ/FgEA:cAnrACAAKAAE

[Zorba]

This is an interesting position. I think few good players nowadays wouldn't hit. It gains significantly in the race, takes away half of opponent's roll, sends another checker back, and advances the backman all at the same time. The high amount of returnshots is a downside, but those returnhits aren't particulary strong and often leave many returnshots themselves.

In 1982 when this quiz was made, pure priming play and slotting were often overrated. This one is a good example. The slotting play leaves opponent a strong direct hit that could get the backcheckers moving away from the not-so-good 22pt anchor. And if missed, there are several rolls giving a good building play on the other side of the board. The slot can only be covered with sixes and if not covered, the slot may have to be lifted next turn, putting that checker in an unfavourable position.

GNUBG 4-ply suggests that not hitting is a blunder, which a 2-ply rollout confirms. Actually making the fourpoint might be better than the slotting play, but that's close. If anything, this looks like the kind of position where the bots excel: a fairly balanced midgame position with both players having ordinary assets and liabilities with nothing extreme going on. So I'm almost 100% sure that the bot is right here.

Rollout:

Spoiler

    1. Rollout          23/15*                       Eq.:  -0.097
       0.517 0.142 0.021 - 0.483 0.143 0.007 CL  +0.011 CF  -0.097
      [0.002 0.004 0.003 - 0.002 0.002 0.001 CL   0.008 CF   0.011]
        Full cubeful rollout with var.redn.
        1296 games, Mersenne Twister dice gen. with seed 921811037 and quasi-random dice
        Play: world class 2-ply cubeful prune [world class]
        keep the first 0 0-ply moves and up to 8 more moves within equity 0.16
        Skip pruning for 1-ply moves.
        Cube: 2-ply cubeful prune [world class]
    2. Rollout          10/4 6/4                     Eq.:  -0.196 ( -0.100)
       0.483 0.150 0.026 - 0.517 0.154 0.005 CL  -0.071 CF  -0.196
      [0.002 0.005 0.003 - 0.002 0.002 0.001 CL   0.009 CF   0.011]
     
    3. Rollout          13/7 10/8                    Eq.:  -0.208 ( -0.112)
       0.487 0.137 0.019 - 0.513 0.154 0.005 CL  -0.080 CF  -0.208
      [0.002 0.004 0.002 - 0.002 0.002 0.000 CL   0.007 CF   0.011]
     

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