The Care and Feeding of a Six-Point Prime
Paul Magriel, 1978
New York Times, March 30, 1978
New Orleans The United States Open, sponsored by the International Backgammon Association, took place last weekend in New Orleans. The winner in the championship section was Gus Michallopoulos, a professor of engineering from Houston, who learned the game many years ago as a boy in Greece. Bill Gause was the runner-up, with Steve Keats and Sandy Lubetkin the semifinalists.

In the consolation, Bob Ciaffone defeated Ellen Jacoby and Median Anderson defeated Patrick Reily to take the last chance. In other sections Ira Hessel defeated Bill Kiehnhoff for the intermediate title; Dee Archer won the beginners; Mel Leifer teamed with Fred Block to win the doubles.

The diagrammed position is taken from Sunday’s 21-point finals match with Michallopoulos (Black) leading Gause (White), 16–13. Michallopoulos had already doubled but was worried: with four of his men deep within White’s home board, he was at a disadvantage. Thus he was visibly relieved when he rolled 4-4’s, certainly his best possible throw.

Black to play 4-4.
He eagerly grabbed a man on the 24-point and quickly played 24/12*/8, running out and hitting White on the 12-point and then continuing on to close his 8-point. Fortunately, he hesitated just before picking up his dice, studied the resulting position, and had second thoughts. Note that in tournament play the rules specify that a move is not officially considered complete until the dice (or at least one die) have been lifted off the playing surface. Indeed Michallopoulos’s hesitation narrowly averted a hasty misjudgment. He found a strategically better play and so replayed his roll.

The correct play is 24/12*, 24/20. The first three 4’s are played as before (24/12*, running out and hitting) but the last 4 is used to bring a man up to the 20-point instead of closing the 8-point. Why not make the 8-point and so complete a solid prime stretching from the 4-point to the 9-point?

(a) 24/12*/8
(b) 24/12*, 24/20
By forming a full 6-point prime, Black could create an impassable barrier for White’s back men. It is often assumed that such a prime will automatically insure victory. Black, however, realized the vital distinction between making the prime and maintaining it. After making the prime, Black’s three remaining men would be stuck deep within White’s home board. Thus there was the danger that Black would be unable to move these back men and as a result be forced to break up his prime.

In fact, more than half of Black’s rolls would force him to break immediately. By playing 24/20 and keeping a man on the 12-point, Black gave himself spare men to play with and so greatly reduced the risk of being forced to destroy his own position while trapped in White’s home board.

In the actual game, White stayed out. Black soon completed his prime and moved out from the 20-point. Black won this game and went on to take the match, 21–16.

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White owns 2-cube
Black rolls 4-4

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Checker play: 2-ply
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4-4: Game BG   Equity
1 24/12*/8 W
+0.5294 x  (a)
2 24/20, 24/12* W
+0.4473 (0.0821)  (b)

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