Three men back

Positions
1

White to move:

DbcjAyCMZ/AADQ:sIFuACAAAAAE

Reasoning and computer analysis ahead, ff you want to take a stab at it without getting spoiled, do it now.

My assessment and GNUbg veridict

At first I looked at 21/13:

  • pros: It brings a chequer to safety.
  • cons: we are behind in the race and our board state is abysmal. We shouldn't run, we should concentrate on building our homeboard and hope to hit one of his chequers.

Then I considered 13/10 13/8:

  • pros: this seems more pure, it starts building what we sorely need, good inner board points.
  • cons: the chequer on 21 could be attacked by the opponent. But on the plus side, it provides contact and if we roll a one we can upgrade our butterfly anchor to a silver point. 13/10 13/8 strips our midpoint, too.

So I went to 13/10 13/8.

I missed 13/5, which is more daring and does not strip the 13.

But GNUbg top pick is 21/16 13/10, every other move is a mistake.
I don't understand what exactly 21/6 accomplishes, is the plan to build outer board points to contain the 24 chequer? Does the 21 cause more trouble (hits) than what it provides (contact)?

2

I'll stab. We're way behind in the race, and gammon losses don't mean much, so I'd first eliminate running with 21/13. Then there's the half-run, which stays flexible at the cost of not staying all the way back. I'd like to take away Black's rolls that make the 5pt, but that wouldn't be the end of the world, and I don't think it justifies hitting loose on the 1pt. That leaves two down as the main candidate. You could slot the 5pt instead, which builds quickly when misses, but against a single back checker we don't need to go all in on the 5pt; the 4pt would be fine too. I'd prefer the flexibility of two down.
So I'd probably play two down. But looking at the answer, it makes sense to jump out. Black's top priority is to bring the back checker around, which makes our priority outfield control. After 21/16 13/10, even if we get hit with a 9, we'll have good sixes from the bar. That's always a perk to watch for, since sixes are usually bad when you're on the bar. I suppose there's also some benefit in jumping over the small prime, which could become a 4-prime soon, and buying a little time to stay pure if we roll 33 or 44 soon.

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3

As usual, many thanks for the reply and detailed reasoning.

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