Endgame Problem 40

A yose problem from Bill Spight - used by permission. The problem has virtually no practical value. ;-) The largest play is only slightly bigger than the second largest, and there are many whole board positions where the second largest play is correct.

However, there are some interesting variations, and figuring out the largest play is a good exercise. :-)

Picky endgame problem (Black to play)  

The outer stones are alive.

Which is the largest play for Black: a, b, or c? How much is it worth?

For a discussion of the solution to this problem, see /Discussion.

BillSpight: Hmmm. I just noticed that the actual solution is not given. Anyone care to give it a try? :-) Solution

KarlKnechtel: Instead of taking a "difference game" approach, I would like to try calculating the miai values for the options. Can we safely say that the solution is the move with the greatest miai value?

Bill: The difference between the best and second best play is very, very small (0.0375 point). Hardly likely to matter. :-)