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Advanced Backgammon #7

Posted By: Nack Ballard
Date: Friday, 24 January 2014, at 9:58 a.m.

In Response To: Advanced Backgammon #7 (Igor)





White is Player 2

score: 0
pip: 161
Unlimited Game
Jacoby Beaver
pip: 162
score: 0

Blue is Player 1
XGID=-b----E-C-AAdC---d-da---B-:0:0:1:21:0:0:3:0:10

32D-51$-21


This is the third roll position (with colors reversed from the fourth roll positions below, so that you could put the player on roll on the near side).

Your rollout result is [N B16 P25] "<=10*5, with the plays being N (Near, 11/10 6/4), B (Both, 24/22 11/10), and P (Point, 11/9 10/9).

Your nacbracs were perfect except you used "S" instead of (the correct) "B" for the 24/22 11/10 play. For a very similar example, refer to 43D-42P-21, which is position #17 (on page 14) of the Nactation tutorial. Other examples of B can be found in the powerful navigation tool "bookmarks" (if that column is not already open, click on the second icon in the far left column), scroll down to "Nactations," click on the + sign next to "B," then check out each of the non-doublets entries.

S (Split-and-down) would be 24/23 13/11, same as the opening-roll play of 21S. [By the convenience clause, you may also use Z (reverse split) for 24/23 13/11. See position #6 at the tutorial link below.] Also, for a comparison of (non-doublet) B, S and Z, see position #62 at the above link, if you didn't already find it with bookmarks.

Most likely, your reconstruction of the fourth roll position is what happened in real life; i.e., that it was reached as above, and prior to the 54 rolled, the third-roll pleyer borderline-blundered with p (point, 13/10), also nactated d (down, 13/10), which XG++ evaluates as a .057 error.

By now, you know from Mike's posts that the capital letters P (Point) and D (Down) are two different ways (one style, the other areal) of nactating 11/9 10/9. The owned 9pt is closer (than the owned 10pt is) to the 6pt. Hence, in both the P and D families, 11/9 10/9 earns the upper-case letter, and 13/10 the lower-case letter.

P (Point) has a dedication clause, which states that the entire play is used to make a point. (Portions of a move that enter from the bar are waived.) Without this clause, silly plays like 11/10 8/6 would rank ahead of 13/10. For more on the dedication clause and the style letters to which it applies, click on the link above and refer to positions #6366 and the "summary of conventions" below #73.

If we optimistically give the players the benefit of the doubt that all moves were well-played throughout, the Advanced Backgammon #7 position below might have been reached by a longer sequence, such as the alternative (in blue typeface) included in the caption.


2O ' ' ' '5X '3X '2X1X4O

2X ' ' '1O4O '4O ' ' '2X
Diagram 1. 32D-51$-21p-54, or 64R-32X-61U-62D-61H-F-52X-4-51D-61R-62$-51P-54

I'm numbering the diagrams the same way Mike did. They depict 32D-51$-21?-54, where the "?" represents p, N, B and P, for diagrams 1 through 4, respectively. (Alternatively, P can be nactated D, or p can be d.) With the roll of 21, the weak move of "p" is represented above. The three best moves (N, B and P) are represented below. In each case, after the 21 move is made, Blue has a 54 to play.

I would make a different play for Blue in each of the diagrams. (I imagine that you expected this sort of diversified response.)

Diagram 1 (above): I have to go with D (Down, 13/9 13/8), though the play recommended in the book, $ (Slot, 13/4), has a nice flare.

Diagram 2: I go with an even flarier play, which is % (alt-slot, 13/9 8/3), only because White has a blot on her 4pt, and there is duplication of both 4s and 2s. (I'm not sure D isn't better even here, but if it's close I love the complications of %.)

Diagram 3: Obviously, P (Point, 6/1* 5/1).

Diagram 4: Surely R (Run, 24/15) is best. It was nice of White not to block this option.

Nack


2O ' '1X '4X '3X '2X '4O

2X ' ' '1O4O '4O ' ' '3X
Diagram 2. 32D-51$-21N-54


2O ' ' ' '5X '3X '2X '4O

1X '1X '1O4O '4O ' ' '3X
Diagram 3. 32D-51$-21B-54


2O ' ' ' '5X '3X2X ' '4O

2X ' ' '1O4O '4O ' ' '3X
Diagram 4. 32D-51$-21P-54

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