Whitney's theorem

Etymology
Introduced by (1907–1989), American mathematician.

Proper noun

 * 1) A theorem stating that two connected graphs are isomorphic if and only if their line graphs are isomorphic, with a single exception: K3, the complete graph on three vertices, and the complete bipartite graph K1,3, which are not isomorphic but both have K3 as their line graph.
 * Whitney's theorem can be extended to hypergraphs.