separates the black stones, hence they cannot run away. a and b are miai.
If Black played , this is the result. Now Black has only one eye.
If Black had answered at , Black can also get only one eye after and .
ichundso?: i dont think that "a" is helpful because black should just ignore this knowing that hes dead and than use the kothreats at "b" and / later on. should be ignored as well, but this would only leave one kothreat , so this is slightly better i think
unkx80: connects outside and escapes. Ugh.