Ko mouth

Creating a ko mouth  

The basic ko rule only forbids recapture of a single stone, so a ko mouth will always consist of two adjacent points. These are all the possible shapes for creating a ko mouth on a conventional board, created by shifting the basic position (a) to an edge or corner; general graph go may open other possibilities.

Linked ko mouths  

Sometimes a ko mouth can be adjacent to another. In the pictured case white can capture in the ko marked with squares only after playing in the circled ko. This kind of situation is called a multi-stage ko.