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White to play.
Attempt 1: Alive in [ko]?
Attempt 2: Worse [ko]?
What if W plays 3 elsewhere in attempt 1?
El Draco: Playing at leads to a worse ko for W I think, though if won she gets two more points. I wouldn't play this way just to get those extra two points though unless you have to to win or if you have enough ko threats that are large enough anyway.
If B exchanges a for b before playing at , then it becomes a comparable result as attempt 1 (+2 points for W) and B has thrown away his free internal ko threat.
at a means that B can play at as an internal ko threat (to start another ko at c if W connects at or continue with the first ko if white connects at c).
In other words, W will have to find one extra external ko threat.
This variation makes a double ko for life (so is still bad)
at circle. When White wins the ko, then black plays at the star point causing a second ko fight.
BobWhoosta: The better term is that white needs to fight two kos to live. If white had double ko for life it would mean he is alive. In this case, white has to win first one ko, and then fight another to live.