Quotient of Group by Center Cyclic implies Abelian

Theorem
Let $G$ be a group.

Let $Z \left({G}\right)$ be the center of $G$.

Let $G / Z \left({G}\right)$ be the quotient group of $G$ by $Z \left({G}\right)$.

Let $G / Z \left({G}\right)$ be cyclic.

Then $G$ is abelian, so $G = Z \left({G}\right)$.

That is, the group $G / Z \left({G}\right)$ can not be non-trivial cyclic.

Proof
Suppose $G / Z \left({G}\right)$ is cyclic.

Then:
 * $\exists \tau \in G / Z \left({G}\right): G / Z \left({G}\right) = \left \langle {\tau} \right \rangle$

Thus:
 * $\exists t \in G: G / Z \left({G}\right) = \left \langle {t Z \left({G}\right)} \right \rangle$

Thus each coset of $Z \left({G}\right)$ in $G$ is equal to $\left({t Z \left({G}\right)}\right)^i = t^i Z \left({G}\right)$ for some $i \in \Z$.

Now let $x, y \in G$.

Suppose $x \in t^m Z \left({G}\right), y \in t^n Z \left({G}\right)$.

Then $x = t^m z_1, y = t^n z_2$ for some $z_1, z_2 \in Z \left({G}\right)$.

Thus:

Similarly, $y x = t^{m + n} z_1 z_2 = x y$.

This holds for all $x, y \in G$, and thus $G$ is abelian, thereby making $Z \left({G}\right) = G$, and thus $G / Z \left({G}\right)$ has one element and is therefore trivial.