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Problem of the Week #116: Solution
08-25-2011
, 10:10 AM
Problem of the Week #116: Solution
(a) Cash game. Black owns the cube. Black on roll.
Black to play 5-4.
(b) Cash game. Center cube. Black on roll.
Black to play 3-2.
Note: All ‘cash game’ problems assume the Jacoby Rule is in effect. That is, you can’t win a gammon unless the cube has been turned.
Back games are, in my view, the most interesting category of backgammon positions. Obvious plays are often wrong and counter-intuitive plays abound. Some real insight and experience are often needed to find your way to the right play. Positions 116a and 116b are just two examples of the sort of clear thinking needed to play back games well.
Problem 116a is not an especially difficult problem, although most players will get it right for the wrong reason.
The classical approach to this kind of position was to play 13/8 6/2*, with the idea that if you were hit, you would fall into a strong back game, while if you were missed, you might even be able to win going forward. Thus hitting represented a “two-way” play: good winning chances no matter what course the game took.
The play is actually correct, but the reasoning is flawed. In fact, Black has virtually no chance of actually timing a back game from here, whether he gets more checkers hit or not. After Black plays his 5-4, he’ll trail by only 18 pips in the race (16 if he elects to hit). In an adequately-timed 1-3 back game, Black needs to trail by 90 pips or more. Even if Black gets hit a couple of times, he won’t have nearly enough timing to play the 1-3 game. Before White starts to break his prime, he has to move his two rear checkers all the way around the board, then bring down the checkers from the midpoint. That represents a lot of turns, probably 10 at the minimum. There’s almost no way Black’s position can hold up for that length of time.
In fact, 13/8 6/2* is just a straightforward attempt to win with a front game. Black is rooting for a fan, after which he can make a good board pretty easily, then root for some aces, deuces, and sixes to jump White’s prime. It’s certainly something of a long shot, but much more likely than winning a busted back game. When the timing to hold a back game just isn’t there, sometimes your best chance is to attempt to win going forward. These can be hard plays to make since any chance of success seems so small. But the chance of success is small for any game plan, so just go ahead and follow your logic.
The lesson of problem 116b is simple: don’t make blocking points against a back game unless there’s some chance of actually blocking your opponent.
The obvious play is 13/8, filling in the last blocking point in Black’s prime. The blot left on the 13-point is of no consequence in view of White’s weak board. However, Black has no need for the 8-point. White has plenty of time to maneuver and build his board with the four spare checkers on his 13-point and 8-point, plus the spare on the 20-point which can be released with any 5 or 6. If he makes the 8-point now, Black will find himself needing to clear it in a few rolls, at a time when White’s board is much stronger than it is now.
Instead, Black has a chance to address the real problem in his position – the open 3-point. It’s true that Black has several builders bearing on the 3-point, and each turn he’s a little less than even money to make the point naturally. But it’s a disaster for him if he never makes the point – then White is in effect playing a 2-3-5 backgame, and Black will be leaving plenty of shots when White’s board may be strong enough to win.
The right play is to go ahead and slot now with 8/3! Not only is White unlikely to hit, but most of his possible hits are too dangerous for him in light of his weak board. If he throws a hitting number, he’ll mostly be better off passing on the hit and just building his position. In effect, the 3-2 roll gives Black a free shot to build the most critical point available.
Solution:
(a) 13/8 6/2*
(b) 8/3
(a) Cash game. Black owns the cube. Black on roll.
Black to play 5-4.
(b) Cash game. Center cube. Black on roll.
Black to play 3-2.
Note: All ‘cash game’ problems assume the Jacoby Rule is in effect. That is, you can’t win a gammon unless the cube has been turned.
Back games are, in my view, the most interesting category of backgammon positions. Obvious plays are often wrong and counter-intuitive plays abound. Some real insight and experience are often needed to find your way to the right play. Positions 116a and 116b are just two examples of the sort of clear thinking needed to play back games well.
Problem 116a is not an especially difficult problem, although most players will get it right for the wrong reason.
The classical approach to this kind of position was to play 13/8 6/2*, with the idea that if you were hit, you would fall into a strong back game, while if you were missed, you might even be able to win going forward. Thus hitting represented a “two-way” play: good winning chances no matter what course the game took.
The play is actually correct, but the reasoning is flawed. In fact, Black has virtually no chance of actually timing a back game from here, whether he gets more checkers hit or not. After Black plays his 5-4, he’ll trail by only 18 pips in the race (16 if he elects to hit). In an adequately-timed 1-3 back game, Black needs to trail by 90 pips or more. Even if Black gets hit a couple of times, he won’t have nearly enough timing to play the 1-3 game. Before White starts to break his prime, he has to move his two rear checkers all the way around the board, then bring down the checkers from the midpoint. That represents a lot of turns, probably 10 at the minimum. There’s almost no way Black’s position can hold up for that length of time.
In fact, 13/8 6/2* is just a straightforward attempt to win with a front game. Black is rooting for a fan, after which he can make a good board pretty easily, then root for some aces, deuces, and sixes to jump White’s prime. It’s certainly something of a long shot, but much more likely than winning a busted back game. When the timing to hold a back game just isn’t there, sometimes your best chance is to attempt to win going forward. These can be hard plays to make since any chance of success seems so small. But the chance of success is small for any game plan, so just go ahead and follow your logic.
The lesson of problem 116b is simple: don’t make blocking points against a back game unless there’s some chance of actually blocking your opponent.
The obvious play is 13/8, filling in the last blocking point in Black’s prime. The blot left on the 13-point is of no consequence in view of White’s weak board. However, Black has no need for the 8-point. White has plenty of time to maneuver and build his board with the four spare checkers on his 13-point and 8-point, plus the spare on the 20-point which can be released with any 5 or 6. If he makes the 8-point now, Black will find himself needing to clear it in a few rolls, at a time when White’s board is much stronger than it is now.
Instead, Black has a chance to address the real problem in his position – the open 3-point. It’s true that Black has several builders bearing on the 3-point, and each turn he’s a little less than even money to make the point naturally. But it’s a disaster for him if he never makes the point – then White is in effect playing a 2-3-5 backgame, and Black will be leaving plenty of shots when White’s board may be strong enough to win.
The right play is to go ahead and slot now with 8/3! Not only is White unlikely to hit, but most of his possible hits are too dangerous for him in light of his weak board. If he throws a hitting number, he’ll mostly be better off passing on the hit and just building his position. In effect, the 3-2 roll gives Black a free shot to build the most critical point available.
Solution:
(a) 13/8 6/2*
(b) 8/3
