# Combinatorics

## Trees

Trees are yet another type of graph. Trees have all the properties of graphs except they must be connected with no cycles. A computer's hard drive directory structure is set up as a tree, with subdirectories branching out from a single root directory. Typically trees have a vertex labeled as the root vertex from which every other vertex can be reached from a unique path along the edges. Not all vertices can be a root vertex. Trees come into importance for devising searching algorithms.

## Resources

### Books

Berman, Gerald, and K.D. Fryer. *Introduction to Combinatorics.* Academic Press, 1972.

Bogard, Kenneth P. *Introductory Combinatorics.* Harcourt Brace Jovanovic Incorporated, 1990.

Bose R.C., and B. Manvel. *Introduction to Combinatorial Theory.* John Wiley & Sons, 1984.

Jackson, Bradley, and Dmitri Thoro. *Applied Combinatorics with Problem Solving.* Addison-Wesley, 1990.

Trudeau, Richard J. *Introduction to Graph Theory.* Dover, 1993.

David Gorsich

## Additional topics

Science EncyclopediaScience & Philosophy: *Cluster compound* to *Concupiscence*Combinatorics - History Of Combinatorics, Enumeration, Binomial Coefficients, Equivalence Relations, Recurrence Relations, Graph Theory