Double Hane Followup
White can connect, since Black threatens a double atari. White can also atari then connect at one of the points a, making a full triangle. If White plays one of the points b Black can atari at the other and force White into an empty triangle.
With the marked stone in place, answering at a invites a double atari at b. White 1 and c are possible defenses. Both invite another atari by Black leaving many cutting points. White b would be bad shape.
Three is also the threshold for the double hane as a response being possible. The loss of three stones outweighs the ponnuki.
Alex Weldon: In Dramatic Moments on the Go Board, Abe Yoshiteru recommends trying out a triple hane?, as shown below, in certain situations, because it is full of fighting spirit, or kiai. Obviously, Black can get a double atari at the point a, so to play this way, White must be prepared to treat these stones lightly. Black can get a ponnuki out of this, so one shouldn't play this unless Black is already strong in the vicinity.
If Black plays the double atari, White will typically connect and become stronger by sacrificing one stone, and if Black captures, White may be able to cut at b, depending on the situation.:
Original Author: Dieter
Something similar from pro game: