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Will the prime collapse?
Posted By: Daniel Murphy
Date: Saturday, 22 June 2013, at 3:09 p.m.
In Response To: Will the prime collapse? (leobueno)
The take is probably clearer to Gnubg 4ply because it has not grossly underestimated Blue's winning chances, and hasn't overestimated White's gammon chances. Play it out and you'll see. Blue's winning chances are quite good. Anything can happen. And usually does^{1}.
How does White's next roll break down?
White has sixteen numbers that enter and hit. But he doesn't win all of these.
White also has numbers like 16 26 25 that reach the bar point. But he doesn't win all of these.
White also has 11 21 that enter and split. But he doesn't win all of these.
White has 51. Who's the favorite?
And White has 9 fanning numbers, after which Blue will most likely make the 4 point (as he also will after any number that hasn't hit). With 2's 4's 5's and 9's to cover, only 16 and 66 can't make the point.
If Blue makes the 4 point, then: if White ends up with two checkers on his 24 point, he will only have 13/36 numbers that run, sixes plus 15; if White is split on the 24 and 23 points, he only has 20/36 numbers that run, fives and sixes; and if White is split on the 24 and 21 points, notice that he still needs two numbers, threes and sixes, to run, so he's still only got 20/36 numbers, plus 15.
So Blue has decent chances to keep two checkers contained. If one escapes, the other may not. If both escape, Blue may still win. Gammons are possible for both sides, although Blue won't actually win many, but he'll win a lot of games with cube, since cube possession is worth a lot here, as it tends to be in prime vs. prime positions where both sides are often just a roll away from a crashing disaster.
As far as the score goes, my recollection is that the 5away all take point for initial cubes isn't much different from money, except that one need to be a little more cautious in taking gammonish positions. That's a little vague, but I also find on the interwebs Masayuki Mochizuki's lecture notes on how to play a 5 point match, in which he answers the question of when to double at 5away all with: In a race, a bit later than in money play (because the redouble to 4 is strong), but in a blitz, somewhat earlier.
^{1}As in this easy gammon win for Blue from here:
The score is 00/5. Blue to play 43.
White 104
Blue 110 Position ID: 2m4HIBDZXgcAMA Match ID: UQmuAAAAAAAE

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