Proposition (Conjugation action). Let GG be a . Define a map G×GGG\times G\to G by

gx:=gxg1.g\cdot x := gxg^{-1}.

Then this defines a of GG on itself, called the .

Remarks

Context. The orbits of this action are the in GG, and stabilizers are centralizers. This action is the mechanism behind the class equation and many counting arguments.