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61P-xxx-21 positions

Posted By: Nack Ballard
Date: Friday, 16 April 2010, at 9:02 p.m.

In Response To: 61P-31P-21? (mtuhtan)


2O ' ' ' '5X '3X '1X '4O

1X '1X ' '5O2O2O ' ' '4X

61P-32Z-21


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

1X1X ' ' '5O2O2O ' ' '4X

61P-51S-21


Paul Weaver and I rolled out (mostly truncated) a lot of 61P-xxx-21 positions. When the second player has SPLIT her back checkers, the position that is most pro-5pt (left-hand diagram) and the one that is most anti-5pt (right-hand diagram) are contrasted below:

61P-32Z-21 [P H27 S29] 5k (full)
61P-51S-21 [U P15 $25 S26] trunc

In other words, Blue should make the 5pt in the left-hand position (where many of White's hitting and point-making numbers are duplicated), but he should come up (24/21) in the right-hand position.

Now let's look at the position you asked about:


2O ' ' '2X4X '2X ' ' '4O

2X ' ' ' '5O2O2O ' ' '5X

61P-31P-21


When Opp has made a point in reply, it depends on the quality of the point. When she has made the 5pt, it costs more to get hit on one's own 7pt (or 5pt), and there is more incentive to split, in order to escape or make an advanced anchor (i.e., to counter the impending prime). With the 5pt, 7pt, 4pt and 3pt made, respectively, the (trunc) rollouts show:

61P-31P-21 [U V9 P16 S17 $83]
61P-61P-21 [P $3 U14 V39]
61P-42P-21 [P $20 S21 V26]
61P-53P-21 [P $31 U45 S62]

Nactation key: U = Up (24/21), V = Variant-Up (24/22 24/23), P = Point (7/5 6/5), S = Split (24/23 13/11), $ = Slot (13/11 6/5). Margins are shown in thousandths of a point (e.g., in the first row U is best, V is -.009, P is -.016, etc.).

I look forward to seeing how close your full rollout result of 61P-31P-21 is to our trunc result. Regardless, the trunc comparisons reinforce the tendencies involved.

Nack

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