Answers to Chow’s Checkerplay Challenge #2

Problem 1: Money play with Jacoby

When this position came up OTB, I played 7/5 and looked around for a 3. But 24/22 is mandatory here, and then the only plausible 3 is 8/5, making the 5pt. I have found it to be a surprisingly good rule of thumb that if your opponent has an advanced anchor while you still have a 24pt anchor, then you must try to get an advanced anchor yourself. Here, White’s strong board would have made me balk at playing 24/22 8/5 and leaving a double shot even if I had seen that play, but actually, White’s strong board makes it even more urgent to get a better anchor.

In the variant position, I have changed the roll to 42, and anchoring on the 20pt comes out on top by a sizable margin (according to XGR+) despite many seemingly plausible alternatives.

Pip counts: White 136, Black 174
Position ID: Zs7CAQbQa/AAMg Match ID: cIkJAAAAAAAA

Pip counts: gnubg 136, tchow 174
Position ID: Zs7CAQbQa/AAMg Match ID: cAkKAAAAAAAA

Problem 2: 4 point match, White 0, Black 0

Pay now or pay later? Answer: Both!

This position was obtained by tinkering with a position that Grunty posted on rec.games.backgammon. Though White’s board will get stronger by the minute, leaving a double direct shot by making the 9pt right away rolls out as a double whopper. Given that, 13/4 would seem to be the natural move, but the rollout favors the unusual move 13/9 7/2 by a clear margin.

In the variant position, I have strengthened White’s board.

Pip counts: White 135, Black 95
Position ID: mM/BYQCrtgMNAA Match ID: QYmSAAAAAAAA

Pip counts: gnubg 127, tchow 95
Position ID: Zs7BYQCrtgMNAA Match ID: QYmSAAAAAAAA

Problem 3: Money play

Pip counts: White 63, Black 99
Position ID: t5sTBABtu0QAAw Match ID: UQkJAAAAAAAA

Problem 4: 1 point match

Pip counts: White 113, Black 106
Position ID: tm0FYAgbnoMHAA Match ID: cAklAAAAAAAA

Pip counts: gnubg 111, tchow 106
Position ID: s20FYAgbnoMHAA Match ID: cIkoAAAAAAAA

Problem 5: Money play

Slot boldly or play safe? If we slot then it is fairly clear that 8/3 7/4 is best since it diversifies our numbers to cover and escape. This diversification is important; see the variant position below, and compare the absolute equity of 8/3 7/4 (+0.332±0.011) in the variant position with the absolute equity of 8/5 7/2 (+0.348±0.010) in the original position. It is clear we gain a lot if the slot works but we also lose big if it does not. I played safe here and the rollout says it was a whopper.

Scoring: Give yourself 1 point if you chose the imaginative play 8/3 6/3.

Pip counts: White 118, Black 103
Position ID: ZpsLA0CbbQ0ADA Match ID: QYkOAAAAAAAA

Pip counts: gnubg 118, tchow 102
Position ID: ZpsLA0CbbQsADA Match ID: QYkOAAAAAAAA

Problem 6: Gammon go (2 point match, White 1, Black 0, Crawford)

Some might be tricked by the score into hitting, but hitting can't be better than making a four-point board. What I found surprising was that downgrading the 4pt to the 3pt and keeping the 8pt came out ahead of making the solid four-prime. Generally, a solid prime is much better than a broken one. However, here White has a just a single checker back and we are not really trying to prime it; we're hoping to attack it by hitting it next turn. The 8pt-6pt-5pt-3pt configuration is better than the four-prime for this purpose; if we make the solid four-prime, then White hops out giving us a single direct shot with 66 65 63 62 61 51 and escapes entirely with 64. If instead we play 6/5(2) 4/3(2), then White hops out with 62 54 53 52 and escapes entirely only with 55; also it gives White a bad 61, and gives ourselves more good hitting rolls.

Pip counts: White 138, Black 125
Position ID: LM/gAxBjnsHBAA Match ID: 8IlEABAAAAAA

Problem 7: Money play

At some point during a blitz, the "local ammunition" starts to run low and we face a tricky decision. Do we keep rushing the nearest available ammunition forwards to try to continue attacking, at the risk of overextending ourselves? Or do we start consolidating by moving our rear checkers into a better position so that we retain a strong advantage even if the blitz fails?

Here it is tempting to keep trying to close out the checker by playing 13/9, but according to the rollout, anything but 20/16 18/16 is a whopper.

Pip counts: White 135, Black 112
Position ID: jOcxA0DbbIEgAw Match ID: QQkKAAAAAAAA

Problem 8: Gammon save (2 point match, White 0, Black 1, Crawford)

I threw this one in for anti-QF purposes. It's gammon save so the natural thing to do is to play safe, and the top play of the rollout is to play safe. (Clearing the 7pt is better than clearing the 8pt because we might still want to attack next turn.)

Pip counts: White 83, Black 91
Position ID: a9tDAASZvc0AAA Match ID: 8AlXAAAACAAA

Problem 9: 1 point match

This is a tricky decision since we haven't gained enough pips to just win the race, and we're forced to play a lot of pips and can't hold on to all our defensive assets. The 6-away point is usually very important for containment (recall Problem 6 above), but our rearmost checker is also valuable, and there's no good way to hold on to both. I decided to hold on to the 6-away point, but the rollout disapproves. Part of what's going on is that uprooting the 6-away point still gives us the 4pt as compensation, which will be very valuable if we subsequently hit White's blot.

Pip counts: White 72, Black 104
Position ID: 294GAAiO3SwhAA Match ID: cIk2AAAAAAAA

Problem 10: Money play

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