# Central Product/Examples/Q with Q

## Example of Central Product

Let $G$ be the quaternion group $Q$ whose group presentation is:

$Q = \gen {x, y: x^4 = e_H, y^2 = x^2, x y = y x^{-1} }$

From Center of Quaternion Group, the center of $H$ is:

$\map Z H = \set {e_G, x^2}$

Let:

$Z = W = \set {e_G, x^2}$

Let $\theta: Z \to W$ be the mapping defined as:

$\map \theta g = \begin{cases} e_G & : g = e_G \\ x^2 & : g = x^2 \end{cases}$

Let $X$ be the set defined as:

$X = \set {\tuple {z, \map \theta z^{-1} }: z \in Z}$