The circled stone is of no concern.
jms: I think we can safely ignore the stone. If is played at , it is gote for black (and a mistake, as the move is uneccesary).
Instead, if black plays at 'a', is still fine. Could B play at b to threaten an eye?
Solution?
jms: There are many possible continuations - but I think B has no eyespace after
Failures
A failed attempt (ko)
Referenced byGokyoShumyoSectio...