Combinatorics is the branch of mathematics studying the enumeration,
combination, and permutation of sets of elements and the mathematical
relations that characterize their properties. As a jumping off point, refer
to:

http://mathworld.wolfram.com/Combinatorics.html

This module provides a pure-perl implementation of nCk, nCRk, nPk, nPRk, !n
and n! (combination, multiset, permutation, string, derangement, and
factorial, respectively). Functional and object-oriented usages allow
problems such as the following to be solved: