Duplicating Saves a Day and a Major Competition
Paul Magriel, 1978
New York Times, July 27, 1978
PARIS — The Curzon House Club’s 1978 Backgammon Championship was held earlier this month in London. This invitational event was limited to 64 players, each paying a $1,000 entry fee. Hermes Michaledes, a Greek Cypriot, took first place by defeating John McManus of Ireland in the finals. Tom Gilbert, a top-ranked American player, easily triumphed over Carrie Trigg to take the consolation flight.

The diagrammed position is taken from the last game of the 17-point consolation finals. Gilbert (Black) had built a commanding 16–5 lead against Trigg (White). With the Crawford Rule no longer in effect, Trigg had doubled on the opening roll. Black has escaped with both his back men and is now in a favorable position. However, White, with four men in Black’s home board, still has good potential to play a back game and hope to hit Black on his way home.

Black to play 5-1.
With the roll of 5-1, Black’s most pressing problem is to protect his three blots in the outfield.
(a) 8/7*, 16/11

The obvious play is 8/7*, 16/11, hitting White’s annoying man on the 7-point. Unfortunately, this gives White too many return shots. White will, in fact, be a favorite to hit back because effectively he has a double shot at Black; almost all 5’s and 6’s enable White both to reenter and hit. By employing the duplication principle, Gilbert found a play that was both safer and more constructive.

(b) 10/5, 6/5
The correct play is 10/5, 6/5, making the valuable 5-point. Because of the blots remaining on the 16-point and 11-point, this move also prepares to give White a double direct shot. However, now White needs the same number, a 4, to hit in either place.

The number that White needs to hit with, 4, is said to be “duplicated.” By duplicating White’s good numbers, Black greatly reduces his chance of being hit. (He is effectively leaving a single direct shot instead of a double direct shot.)

In general, if you must leave blots exposed in twin parts of the board, leave them exposed to the same number, thus minimizing the amount of combinations that hit.

XG logo
Tom Keith 2013 
Match to 17
White 5, Black 16
Black owns 2-cube
Black rolls 5-1

1296 games with VR
Checker play: 2-ply
Cube play: 3-ply Red

5-1: Game BG   Equity
1 10/5, 6/5 W
+0.0606 x  (b)
5 16/11, 8/7* W
−0.0726 (0.1332)  (a)

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