| Checker Problem |
Jeff Ward When is a seven-point prime better than a six-point prime? Surprisingly, every once in a while. Most players with even a little experience would probably answer "never" to this question. Since a six-point prime is an impassable barrier for opponent's men trapped behind it, what possible purpose could there be for a seventh point?
In the diagram, Black hit a shot very late in the game and now has one of White's men trapped. Since Black will usually lose with only one of White's men closed out, Black's immediate goal is to hit and trap at least one other checker.
If Black can close out two men, he becomes a heavy favorite to win; with three, the game is Black's by redoubling, as White would be foolish to accept.
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| Black to play 4-2. |
Black needs to buy some time but should reject breaking his prime by playing 7/1. This move is simply too dangerous as a quick entry and exit by White could lead to a gammon or backgammon.
Instead, Black should play 14/8, completing a seven-point prime! The reason for this seemingly bizarre move is that, Black would ideally like to see his entire prime backed up one point. By making the eight point, Black is actually preparing to move the prime backward. With the first 1, Black completes the process by moving 2/1, breaking the two point.
The retreat of his prime gives Black a much improved situation. White now has almost twice as many numbers which come off the bar; and the sooner White enters, the sooner he can break the twenty-two point.
Another advantage for Black is that it helps him stall. With two blots in his home board instead of one, there is a better chance that White will come off the bar and hit Black, starting another Black checker recirculating around the board.
Once the prime is backed up, Black patiently tries to recirculate his men until the desired results are achieved. For example, if White enters but does not break, and Black has moved past the twenty-two point, Black should hit White's stragger to put him back on the bar. With Black's blots once again on both the one and two points, White again has two numbers which hit and give Black a chance to return to the twenty-four or twenty-three point.
Likewise, should White break and Black miss the shot, Black must hit in his home board at the first opportunity. This not only allows Black to recirculate a man back for another shot, but prevents White from safetying his blots by making a new point.
In general, a prime extending from the three through the eight point is the ideal blocking formation in endgame situations when the objective is to trap an additional man. By slotting the one and two points with two extra men, keeping the third in reserve, the recirculating "machine" operates at peak efficiency.
Rarely, of course, will the perfect formation exist exactly when it is needed. Sometimes, however, if an existing prime happens to be advanced one point too far, it can be backed up with the unusual technique of first making a seven-point prime.