| |
|---|---|
| 21S-65R-52 | |
I recommend that you first read Tim's excellent comments. I agree that the fourth checker on the 8pt is commonly underrated (a concept discussed several times in my/Paul's book), though this extra spare has less impact against one back checker -- it doesn't restrain a natural split. Most of that spare's value for Blue after he plays D (Down, 13/11 13/8) in this position is that his doublets will play better next roll.
It is better understood these days that splitting against a four-checker 8pt should be avoided (and the bigger the split the worse it is). Here, White has only three checkers on the 8pt, so Blue can feel free to split or move up to the 22pt, 21pt or 20pt. HOWEVER, moving out to the 18pt is qualitatively different, because it unleashes the power of the sixth checker on White's midpoint.
Granted, when White has only one checker back, an exchange of hits becomes more attractive for Blue, and coming out to the 18pt increases the chance of that happening. OTOH, White is already split to the 23pt, so going to the 18pt is less of an upgrade in that regard (than splitting off his 24pt anchor with a 6 would be). The point is that many people consider only the exchange-of-hits factor and not the extra-midpoint-spare factor. They offset. Consider, for example, that opening 64S is a tinier error (if error at all) than 65R-64S.
I promised you a rollout; I'll post it separately.
Nack