which is a generating function:
$f[G](x) \equiv \texttt{number of ways to color $G$ with $x$ colors} \cdot x^n$

If we have a single vertex $K_1$, then $f[K_1](x) = n x^n$, since we can color
the single vertex with the $n$ colors we have.
#### § Composition of chromatic funcions of smaller graphs

#### § The chromatic function is a polynomial