Conjugation action on itself
A group acts on itself by conjugation g·x = gxg^{-1}
Proposition (Conjugation action). Let be a group. Define a map by
Then this defines a group action of on itself, called the conjugation action.
Remarks
Context. The orbits of this action are the conjugacy classes in , and stabilizers are centralizers. This action is the mechanism behind the class equation and many counting arguments.