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Proposed standard notation for backgammon plays

Posted By: Tom Keith
Date: Saturday, 27 September 2014, at 7:48 p.m.

This is a continuation of a previous thread which has become rather overindented. It is my revised description of a suggested standard notation for computers to use when writing backgammon plays.

Start with the collection of simple moves that describe the play. Place an asterisk after any move which hits.

  1. Sort the moves in descending order by each move's from point. Then, if there is a tie, sort the tied moves in descending order by each move's to point.

  2. Combine sequences. Starting with the first move in the play, look for a later move whose from point is the same as the earlier move's to point. If found, combine the two moves into one with the combined move taking the place of the earlier move. For example,

    24/18, 18/13  →  24/18/13

    13/7*, 7/5  →  13/7*/5

    There is no limit the number number of moves that can be combined.

    9/7, 7/5, 5/3, 3/1  →  9/7/5/3/1

    9/7*, 7/5, 5/3, 3/1  →  9/7*/5/3/1

  3. Remove unadorned intermediates. If the internal point number of a combined move does not hit, remove that number from the combination. For example,

    24/18/13  →  24/13

    24/18/13*  →  24/13*

    9/7/5/3/1  →  9/1

    If an internal point does hit, do not remove the point number.

    13/7*/5  →  13/7*/5

    9/7*/5/3/1  →  9/7*/1

    A hit that has been marked by an asterisk earlier in the play does not have to be marked again later. When an asterisk is omitted like this, its point number can be omitted as well if it is an internal point.

    6/5*, 6/5*/3  →  6/5*, 6/5/3  →  6/5*, 6/3

  4. Combine parallel moves. When two moves begin and end on the same point, they may be combined into one move. Add a number in parentheses after the move indicating the number of checkers that move together.

    24/18, 24/18, 13/7, 13/7  →  24/18(2), 13/7(2)

    6/5, 6/5, 6/5, 4/3  →  6/5(3), 4/3

    2/off, 2/off, 2/off, 1/off  →  2/off(3), 1/off

    6/5, 6/5, 6/5, 6/5  →  6/5(4)

I have written a quickie C program to try it out. (Source code here.) It seems to give sensible results. One possible objection might be this play: "13/10*/7, 13/7", which Taper Mike would prefer to see written as "13/10*/7(2)".

The following table shows the results of my tests:

Original Sort Sequences Remove Internal Parallels
24/20*, bar/20 bar/20*, 24/20
20/18, bar/20 bar/20, 20/18 bar/20/18 bar/18
20*/18, bar/20 bar/20*, 20/18 bar/20*/18
24/18, 24/18, 13/7, 13/7 24/18(2), 13/7(2)
24/22, 22/20, 20/18, 18/16 24/22/20/18/16 24/16
18/16, 24/22, 22/20*, 20/18 24/22, 22/20*, 20/18, 18/16 24/22/20*/18/16 24/20*/16
13/9, 13/10 13/10, 13/9
7/6, 6/5*, 6/5, 5/4 7/6/5*/4, 6/5 7/5*/4, 6/5
6/5*, 6/5, 5/4, 4/3 6/5*, 6/5/4/3 6/5*, 6/3
24/21, 7/4*, 4/1*, 7/4 24/21, 7/4*, 7/4, 4/1* 24/21, 7/4*, 7/4/1* 24/21, 7/4*, 7/1*
24/21, 7/4*, 4/1, 7/4 24/21, 7/4*, 7/4, 4/1 24/21, 7/4*, 7/4/1 24/21, 7/4*, 7/1
13/7, 13/10*, 10/7 13/10*, 13/7, 10/7 13/10*/7, 13/7
13/7*, 13/7 13/7*(2)
13/9, 9/5, 5/1, 9/5 13/9, 9/5, 9/5, 5/1 13/9/5/1, 9/5 13/1, 9/5
13/9, 9/5*, 5/1, 9/5 13/9, 9/5*, 9/5, 5/1 13/9/5*/1, 9/5 13/5*/1, 9/5

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