Yes, Modern Backgammon is the source. I love the problems, but dislike some aspects of the organization. The "middling plays" suggestion is a particular peeve. Robertie writes (p6):
"If the nets were human, they would tell you that they guide their play according to four fundamental principles of maneuver. Arranged roughly in order of importance, the four principles are these:
- Efficiency
- Connectivity
- Non-Commitment
- Robustness"
The latter three are positional concepts--they make sense and are well presented. "Efficiency" is a catch-all that someone translated for me as "make the highest equity play."
Efficiency is classified into "seven rules" (pp25-7):
- Relative board strength determines risk tolerance.
- Balance risk and reward. Examine middling plays.
- Stacks of checkers are enormous weaknesses.
- Avoid dead checkers. Utilize semi-dead checkers as quickly as possible.
- Avoid front-loading your structure with spares.
- Counter weak structure with strong structure, thus hastening the crisis point.
- See out unambiguous improvement.
Of these rules most are positional; 2 and 7 are not and 2 is particularly silly. A middling play sounds like something between the best and worst play.
Here is one of Robertie's examples (diagram 2-10 p30).
He identifies three candidate plays: the "brute-force solution" of 11/7(2); the "safe play" of 12/6 13/11; and the "middling play of 13/9 11/9(2)!" [Robertie's exclamation point]. XG++ slightly prefers the safe play (I'm not going to bother with a rollout):
                         |
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| XGID=--BBCdD----BAA--a-bcbab---:0:0:1:22:0:0:3:0:10 | |||||
| Blue to play 22 | |||||
| 1. | XG Roller++ | 13/11 12/6 | eq: +0.848 | |||
| ||||||
| 2. | XG Roller++ | 13/9 11/9(2) | eq: +0.836 (-0.012) | |||
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| 3. | XG Roller++ | 11/7(2) | eq: +0.654 (-0.195) | |||
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eXtreme Gammon Version: 2.10
I still recommend the book highly, but there are some quirks...