This strange shape rarely occurs in practice, but is interesting enough to discuss.
, play on the point of symmetry, sets up a throw-in ko at a. On the other hand, it gives Black a chance to start his own throw-in ko at b.
If White starts the ko and win it, she gets 28 points of territory. If Black starts the ko and win it, he gets only 8 points of territory. So the burden is much heavier on Black - in most cases, White should play and wait for an appropriate moment to start the ko. That will considerably restrict Black's play elsewhere - he can't worsen the ko threat situation.
(The position is somewhat similar to a more common shape called "ten thousand year ko" in nature.)
And strangely, neither side can erase the ko possibility in one move. is not advisable - it doesn't stop White's throw-in at a. Worse,
increases White's territory (or decreases Black's territory) after the ko fight by 1 point.
forces
- else White plays there and wins. This abandons the ko possibility which is normally advantageous for White, though it may be played as a ko threat or game-end procedure.