\begin{definition}[Definition:Generating Function/Extraction of Coefficient]
Let $\map G z$ be the generating function for the sequence $S = \sequence {a_n}$.
The '''coefficient of $z^n$ extracted from $\map G z$''' is the $n$th term of $S$, and can be denoted:
:$\sqbrk {z^n} \map G z := a_n$
\end{definition}