Beginner Exercise 51 / Solution
The page Two Space Notchers Not Fully Connected has discussed the shape quite extensively, so the explanation will be quite brief here.
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.