HowToLose [5k]: After the marked black stone, is it possible for W to win the race? I put this here not simply because it is a semeai, but because of the surrounding positions; unfortunately, I'm not good enough yet as to be able to think globally enough to answer this question myself.
kb: At first glance, I see it as a seki, because it is too risky for Black to try and kill the White stones.
Black should take a liberty with and let White fill the ko at , turning the entire position into seki.
If Black tries to play the ko by making a threat, say at , then White will play at , turning the entire situation into a direct ko with White taking first through the sequence to , because of the local ko threat White has at . White will then ignore any ko threat Black plays and take with .
If Black omits the exchange at on the second diagram and just takes outside liberties, White will take at and then play regardless of where Black plays and then play to live (Black cannot play there because of damezumari.
If White does not fill at on the second diagram, then White will die by double ko (after White fills at then Black will play at a to kill White).