The page Two Space Notchers Not Fully Connected has discussed the shape quite extensively, so the explanation will be quite brief here.
is the vital point. If
,
makes a and b miai.
The answer to the hane at is to play at
, making a and b miai.
makes a hane on the other side. In this case, Black can live with
. Beware,
cannot play at a. To find out why, please refer to Beginner Exercise 14.