I will add a nice example that lightvector showed me today:
Assume black has infinite ko threats so has the luxury of leaving that ko open. Can he claim the extra point of territory of not playing C9 to defend and kill everything?
This is almost the same as life and death example 9: Article 1. The game of go
It seems very likely, the way the Japanese pros justify their reasoning and just like the above three positions are explained by pros, that this extra liberties do not change the life and dead example 9, and it is still ruled as black needing to defend.
If you apply J2003 however, white stones are dead (not uncapturable, not capturable-1, not capturable-2) but all the black stones are capturable-2 (white wins the capturing race easily if they play first, thus controlling the whole corner, thus black stones are neither uncapturable nor capturable-1. But the local-2 covers the whole corner up to the outer black group, and thus it is easy for black to add extra stones here on the outside, and similar to the F19 stone in the above three examples, J2003 model counts that as “enabled” by the dying black group and thus the group is capturable-2 and thus alive. There is the capturable-3 exception that is meant to cover exactly some other examples very similar to this one, but in this one the ko stone is not capturable-3 and thus the model deems black simply alive). Thus under J2003, black does not need to defend.
I have thought of an alternative formal definition for which stones count as “enabling”, but I have been unable to get a definition to match all of these:
- The seki in life and death example 2
- The 3 points without capture position
- The above three examples I posted before
- This lightvector example
Normal snapbacks and such are easy because you can specify that the player manages to control an intersection right under the group. The essential hard cases why one can’t simply “drop” the “enable new stones” rule of 1989 (or replace it with the simple rule that it enables control of the intersection right under the original stones, that is, local-1) seem to be positions similar to the three points without capture and the seki in life and death example 2.