Black must find a way to either play all of the points marked x or make an eye on the outside. is the only first move.
For the correct solution to this problem see Xuanxuan Qijing Problem 2/Solution
If white descends with , black cuts and the sequence to
is forced, allowing black to play one of the three points in sente.
is necessary for later. Playing
in exchange for
, as shown in the diagram, is an error.
Black continues by playing another of the three points with . Because of the marked stones, this is sente. If white plays
,
-
captures white's surrounding stones.
Herman Hiddema: This fails if white plays at
, black is short on liberties. Blacks exchange of
(marked black stone) for
(marked white stone) in the first diagram is premature.