In this diagram, is a contact play which aims at sabaki. If Black responds with the hane at , then is the bulge move. If Black gives atari with , then sets up the ko. For White to connect against Black's atari may be slow or heavy. White may aim to enlarge the ko by playing a or b.
The techniques involved in setting up and fighting a bulge ko are relevant to many middle game sequences and corner invasions (for example: 4-4, 6-3 Enclosure, 3-3 Invasion)
For more information see: