Editing Chromatic polynomial (section)

==History==
[[George David Birkhoff]] introduced the chromatic polynomial in 1912, defining it only for [[planar graph]]s, in an attempt to prove the [[four color theorem]]. If <math>P(G, k)</math> denotes the number of proper colorings of ''G'' with ''k'' colors then one could establish the four color theorem by showing <math>P(G, 4)>0</math> for all planar graphs ''G''. In this way he hoped to apply the powerful tools of [[mathematical analysis|analysis]] and [[abstract algebra|algebra]] for studying the roots of polynomials to the combinatorial coloring problem.

[[Hassler Whitney]] generalised Birkhoff’s polynomial from the planar case to general graphs in 1932. In 1968, [[Ronald C. Read]] asked which polynomials are the chromatic polynomials of some graph, a question that remains open, and introduced the concept of chromatically equivalent graphs.<ref>{{harvtxt|Read|1968}}</ref> Today, chromatic polynomials are one of the central objects of [[algebraic graph theory]].<ref>Several chapters {{harvtxt|Biggs|1993}}</ref>