Examples of Sabaki
From a game between Jowa (White) and Hattori Rittetsu. According to Hashimoto Utaro, - is an instructive example of Jowa's cleverness at sabaki. White can sacrifice and play the vital point a in sente if Black tries to undercut the white group.
Velobici: Could someone add an example of the possible Black undercut of the White group and then supplement that with how prevents the undercut from succeeding.
Suppose white just plays . Now when black decends to white blocks at to keep some eyespace for her group, but since black doesn't have to respond to , he gets another move. In other words, is forcing, but is not. In the sabaki example, a move by black at x is forcing, but white's reply at a is also forcing. This sacrifice to gain tempo? is a standard technique. For additional information see this example and chapter 10 of Tesuji by James Davies.