 The pioneers in this area of mathematics were George Pólya, Arthur Cayley  and J. Howard Redfield.In some graphical enumeration problems, the vertices of the graph are considered to be "labeled" in such a way as to be distinguishable from each other, while in other problems any permutation of the vertices is considered to form the same graph, so the vertices are considered identical or "unlabeled".In general, labeled problems tend to be easier.