a and b being miai.
Robert Pauli: The original solution plays at a and, of course, at b, but this one creates more ko threats (if kept in reserve, of course). Not the topic, but anyway.
Robert Pauli: Here's why (above) shouldn't capture the stone (side topic):
Ko fights after each white move skipped. Pretend that Black loses each and has no escape.
But even if Black had no hope to win the ko,
a ko wouldn't be in the "rules":
after capture, the eye must be unconditionally undividable.