ABSTRACT
The subject of graph colorings was born in 1852, when Guthrie asked whether every planar map could be colored using at most four colors in such a way that two regions that share a border of positive length receive different colors. In 1976, the first correct proof of this conjecture was established by Appel and Haken [4]. During the hundred years leading up to this proof, a body of theory was developed in the language of graph theory concerning partitions of the vertex set of a graph.
