EndgameProblem42/attempts

White first  

After we can expect all of this in sente. Let's count this as -5.5.

Black first, sente  

After this sente sequence, the marked point is 0.5 for White and Black makes 3 extra points, for a total of 2.5

Black first, gote  

If White leaves it after in the previous diagram, then Black has at least this sente sequence, or a big ko.

With respect to the original diagram, White loses 5 points and Black gains 2. SO the count here is +7

Black first  

Assuming A-B later, here keeps the score at -2.5

This gives the following tree:

                 0.5 (6.25)
               /    \
              7(9.5) -5.5
             / \
            7  -2.5

and the value of the move is approximately 6.25

If Black is komaster, then it could be asmuch as a 8 sente.