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64P-41, Nactation correction

Posted By: Nack Ballard
Date: Thursday, 23 April 2015, at 4:54 a.m.

In Response To: 64P-41, Nactation (Timothy Chow)





White is Player 2

score: 0
pip: 157
Unlimited Game
Jacoby Beaver
pip: 167
score: 0

Blue is Player 1
XGID=-b----E-C---eE---b-d---bB-:0:0:1:41:0:0:3:0:10

Blue to play 41


First and foremost, I must sheepishly confess that even I screwed up here. Actually...

.....D = 13/9 8/7
......d = 13/8

There is a "wrinkle" in the 6pt convention that applies to the outer board, which states that the blot/spare destination further from the 6pt ranks higher. However, the wrinkle doesn't actually change the ranking of the plays in this case! If closer-to-the-6pt were the rule, the 7pt blot would beat the 8pt spare. As it is, the 9pt blot (further from 6pt) beats the 8pt spare (for the same result).

Taper Mike once pointed out to me that for 64R-xxx-63, 14/11 13/7 outranks 14/10 13/8, contrary to the two plays' relative strength. He suggested that, in order to achieve the more favorable result, the wrinkle could be modified from the (current) "further from the 6pt wins" instead to "closer to the 6pt loses." At the time, it did not seem worth adjusting the rule just for this situation (especially given that (a) the vast majority of the time the same result is produced, and (b) after the 7pt is made, the situation reverts to the spare on the 7pt being better than the spare on the 8pt). However, now that I see that the same inferior ranking exists for the more common cases of (a non-hitting) 41D/d and 21D/d, I believe I will adopt Mike's suggestion (for the next update).

In the meantime (i.e., until I make the change), I suggest avoiding the D family when the entire roll is used to move a single checker to or within the outer board. Or, if you like using D even under those circumstances, add a DOT after it (D.) to indicate that you are using assumption. That is, an after-dot means that you are conveying the obvious play in the indicated family.


Aside from that temporary oddity, your reasons for preferring the D family are valid. Add to that that there is some fine print in the use of "style" letters (T is a style letter), though it mostly comes into play only in a small minority of positions. Following this paragraph are some counterarguments.

D (Down) is an "areal" (area-based) letter. Areal letters are clear in their usage, though (compared to style letters) it is more likely that other plays in the same family will exist, the ranking of which can require an understanding of the 6pt convention.

64P-41 (diagram repeated above, for convenience) is a case in point. With a roll of 41, there is only one point upon which a checker can be sTacked, and therefore it is quickly and abundantly clear (putting myself in the shoes of whoever might be reading my Nactation) that T (sTack/Tower) must mean 13/8.

By contrast, there are two ways to play 41 that fall within the D family. Which is assigned the upper-case "D" and which the lower-case "d"? Even IF closest-to-7pt-loses was already in effect and the correct answer was therefore D = 13/8 and d = 13/9 8/7, to be certain of that one would have to know the 6pt convention and its application of its "wrinkle." It is very unlikely anyone would play 13/9 8/7, and so some might argue that it doesn't matter -- an unsophisticated interpreter will simply think "Oh, Tim must mean 13/8, because it is the only Down-family play that makes any backgammon sense." But I'm sure you can appreciate that less obvious examples can arise! Moreover, there needs to be some way to unambiguously represent poor or aberrant plays -- to refer to weaker legal plays in general.

It makes a difference how familiar an areal letter is likely to be to the interpreter. "D" is one of the basic letters introduced in section 1 of the Nactation tutorial, whereas examples of non-doublet "0" do not appear until section 4. With that in mind (and to use an example that does not happen to have the misfortune of the aforementioned oddity), imagine instead the roll being 43 with a play of 13/6. Even you would probably choose T (sTack/Tower) or 6 (destination 6pt) rather than the areal letter O (Outer -- which means that half the play is made into the outer board and half is made out of the outer board). Not only is O "bi-areal" (which is why the uni-areal letter D is taught earlier), but also there are three plays in the O family (thus technically one would have to know the 6pt convention in order to correctly relegate upper-case O to 13/6, lower-case O to 13/9 8/5, and upper-case italic O to 13/10 8/4).

I often prefer style letters because they describe a clear, easily understandable action, and there is frequently only one play that fits said action. Consider 52D-64H for 24/14* (H = Hit, rather than the areal R = Run) or 52S-64H for 13/3* (H = Hit rather than the areal O = Outer). Granted, some actions stand out more clearly than others.

Additional reasons that one might prefer "style" letters to "areal" letters are listed in the tutorial at the beginning of section 6.

Nack

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