---
categories: Combinatorics
---

## Problems
- [Chemistry](https://neerc.ifmo.ru/past/2012/northern/problems.pdf)
- [Bus Routes](https://archive.algo.is/camps/mipt/2015/day6/A/statement.pdf)
- [The Child and Binary Tree](http://codeforces.com/contest/438/problem/E)

## See also
- [Pólya enumeration theorem]()
- [Cycle index]()
- [Generating function]()

## External links
- [Introduction to the Theory of Species of Structures](https://bergeron.math.uqam.ca/wp-content/uploads/2013/11/book.pdf)