Weisfeiler Leman graph isomorphism test

In graph theory, the Weisfeiler Leman graph isomorphism test is a heuristic test for the existence of an isomorphism between two graphs G and H. It is based on a normal form for graphs first described in an article by Weisfeiler and Leman in 1968. There are several versions of the test referred to in the literature by various names, which easily leads to confusion.