                       |
| ||||
| XGID=--BaBABA----aB--bbbcbbB-BA:1:1:1:31:0:0:3:0:10 | |||||
| Blue to play 31 | |||||
eXtreme Gammon Version: 2.03
It's tough to know what's going on in priming games and what to read into the rollouts when the plays are so close. A single roll can be enough to tip things one way or the other.
In my original response I noted White's 55, 33, and 11 as reasons not to hit, as they represent an 8% chance to force him to break his prime immediately if he is not on the bar. This lead me to 7/6 with the 1, as I wanted to hold all blocking points and didn't want to play 5/4. I didn't consider 6/5, and I didn't understand why it performed so well, since the shift allows White to hold his prime with 33. After looking at this a bit more deeply, I see that getting White to break his prime, particularly on 33, is not as large a victory as I believed.
If White rolls 55 Blue's timing is immensely improved. If White rolls 11, Blue's timing remains tenuous. But 33 is a 'tweener.
If Blue plays 7/6, White is forced to break his prime with 33, but he is able to keep the back of it slotted, so when Blue hops with a 6 to preserve his timing, he's forced to hit, giving back the timing he's gained by allowing White to recycle.
If Blue instead plays 6/5, White isn't forced to break his prime with 33, but he has to hit if he wishes to keep it. The "forced" hit improves Blue's timing substantially. And unlike the 7/6 variation, Blue isn't forced to give that timing back by allowing White to recycle. This and the fact that 33 is a larger than average roll, give Blue a better chance of holding the fort until White's prime gives way, especially if Blue can dance a turn or two.
I thought I was being clever by blocking White's 33 and forcing him to break his prime. But according to XGR++, forcing White to hit with it instead gains Blue over 0.121 equity on that one roll.