**Graph Theory Primer**

Prepared by:

Joseph Malkevitch

Department of Mathematics and Computer Studies

York College (CUNY)

Jamaica, New York

email:

__malkevitch@york.cuny.edu__

web page:

__http://york.cuny.edu/~malk__

*Theorem:* The sum of the valences of a graph equals twice the number of edges of the graph.