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Nactation  How can a running play belong in the S (Split) family?

Posted By: Taper_Mike
Date: Wednesday, 19 June 2013, at 8:48 a.m.

In Response To: OLM 2013-06-18 (Michael Sullivan)

In Nactation, Split is one of the areal families. Membership is determined by the areas of the board where checkers are moved. For this purpose, each die is considered independently.

There are four board areas used by the areal families:

1. Far  The entire movement takes place on the far side of the board, including entry from the bar. The checker lands somewhere between the 24pt and 13pt.
2. Down  A checker is moved to or entirely within the outer board. It must land somewhere between the 12pt and 7pt. So long as it lands in the outer board, it may be moved from any point between the 18pt and 8pt.
3. Jump  A checker is moved from the outer board into the inner board, by jumping over the bar.
4. Inside  A checker is moved entirely within the inner board, including bearing off.

The definition of the Split family deviates from these areal definitions somewhat. It requires, for a roll of non-doublets, that the larger die be played on the far side of the board (as defined above), and that the smaller die be played from the far outer board into the outer board. That is, smaller die must be used move a checker from a point between the 18pt and 13pt to a destination between the 12pt and 7pt.

This definition handles most of the normal splitting moves that are made in the early part of a game, for example, 62S, 63S, and 64S. In many circumstances, however, a play that moves checkers according to the definition of the Split family will not resemeble a split in any way. Todays play in the OLM is one of them.

 White is XG Roller++ score: 2 pip: 172 5 point match pip: 174 score: 4 Blue is BGO Readers
XGID=--b---DbC-a-cD---aCdA--b--:1:1:1:65:4:2:0:5:10
Blue to play 65

When this 65 is played 20/9, there are two checker movements, 20/14 and 14/9. The first, 24/14, occurs on the far side of the board. The second, 14/9, moves from the far outer board into the outer board. Thus, 20/9 belongs in the Split family.

Incidentally, when both dice are used to move a single checker the full distance of both dice, for purposes of Nactation, it is considered that the larger die was played first. The only exceptions to this come when an intervening block requires that the smaller die be played first, or it is necessary to play the smaller die first in order to make or avoid a hit.

By this rule, it is not allowed to treat 20/9 as though it had been played 20/13, 13/9. In practice, that means that 20/9 cannot be a member of the Reverse Split family. (Reverse Split is the family that plays the smaller die on the far side of the board, while moving the larger die from the far outer board to a destination in the outer board.)

A comparison of the families Split, Reverse split, and Both can be found in this post:

Nactation  Clarifying S (Split), Z (Reverse split), and B (Both)  Updated Dec. 2012 BgOnline Message No. 134754

It includes additional examples of plays in the Split family that do not split, as well as an explanation of how these families are used for a roll of doublets.

Hope this helps.

Mike

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