Definition:Conjugate (Group Theory)/Element

Definition
Let $\left({G, \circ}\right)$ be a group. An element $x \in G$ is conjugate to an element $y \in G$ iff:


 * $\exists a \in G: a \circ x = y \circ a$

Alternatively, we can say that $x$ is the conjugate of $y$ by $a$.

This relation is called conjugacy.

We write $x \sim y$ for $x$ is a conjugate of $y$.

This relation is alternatively (and usually) expressed as:
 * $x \sim y := a \circ x \circ a^{-1} = y$

which is seen to be equivalent to the other definition by taking the group product on the right with $a^{-1}$.

Also defined as
There is another way of defining conjugacy of elements, which is subtly different:

$x$ is a conjugate of $y$ iff:
 * $x \sim y := \exists a \in G: x \circ a = a \circ y$

or:
 * $x \sim y := \exists a \in G: a^{-1} \circ x \circ a = y$

This is clearly equivalent to the other definition by noting that if $a \in G$ then $a^{-1} \in G$ also.

Also known as
Some sources call $a \circ x \circ a^{-1}$ (or $a^{-1} \circ x \circ a$) the transform of $x$ by $a$.

Also see

 * Conjugacy is Equivalence Relation
 * Definition:Conjugacy Class