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Opening 5-2: 24/22, 13/8 ??

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Apr 4, 1995, 3:00:00 AM4/4/95
Hi all,

A couple of weeks ago, Kit Woolsey posted the following, summarizing the
results of opening moves experiments using computer backgammon programs:

"5-2: The normal play for years has been 13/11, 13/8. However the newer
splitting play, 24/22, 13/8, (shunned because of the crushing 5-5 threat)
has come out a bit better. The slotting play of 13/8, 6/4 (which used to
be my choice) did not survive the rollouts -- it was clearly inferior."

I'm no expert, but the possibility of 24/22 13/8 being better than 13/11,
13/8 baffles me. 5-5 is only 1/36, and it's only really crushing when
it's followed by a dance, 1/4 of the time -- total parlay, 1/144.
Therefore, I've been thinking about the other merits of 24/22 13/8:

1.) Building rolls: The best building rolls available to the back checkers
after the split are 3-1, 4-2, and 6-4. However, these are all excellent
rolls anyway after 13/11 13/8. 3-1 makes the 5-pt, 4-2 the 4-pt, and 6-4
the bar point. Furthermore, both 3-1 and 4-2 (and 6-4, for Jellyfish
fans!) leave the player who split with a choice between good alternatives.
Why duplicate good rolls?

2.) Other rolls containing a 2: These make the 22-pt after the split,
which is nice, but not nearly as nice as the 21-pt or 20-pt. It seems
that pursuing the 22-pt would be more important after the opponent has
built a decent prime. Note that by making the 22-pt, the player reduces
the chance of later making the 21-pt or the 20-pt. Meanwhile, after 13/11
13/8, a 2 makes the 11-pt. It may not be as important as the 3-pt, but
it's nice to have, since it's 6 away from the 5-pt. Therefore, it helps
both in offense - making the 5-pt - and in defense - fighting an opponent
who's made the 5-pt.

3.) All other rolls: the only other roll that seems like it might be
better after the split is 5-4, which escapes a back checker to the 13-pt.

4.) Other potential advantages of a split: discourage opponent's outfield
development; opponent gains nothing from hitting loose on the 22-pt

Overall, the only explanation that makes sense to me is that the computer
programs place more value on a good defense than a good offense. Is
anyone familiar with how they play 3-1 or 4-2 after the split? What about
early 2-2 or 3-3: do they move the defensive anchor forward or attack?
Can anyone figure out any other reasons why the split might be good?



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