Binomial Coefficient

WIP Defintion

Binomial Coefficient is used to determine the number of unordered
combinations of k length from a set of n possible choices.

\begin{equation} ^{n}C_{k} = \frac{n!}{k!(n-k)!} \end{equation}

Algorithm Implementation

Below is an implementation of the binomial coefficient in lisp. I
don't remember the source for this, at least the lisp version. I found
a stackoverflow answer on the binomial coefficient that lead me to
finding the lisp version. I haven't found the lisp version yet.

(defun choose (n k)
   (if (= k 0) 1
       (/ (* n (choose (- n 1) (- k 1))) k)))

References