X Köchendorffer, L.A. Kalu: lnin and their students in the 50s and 60s.
Nowadays the most deeply developed is the theory of binary invariant
relations and their combinatorial approximations. These combinatorial
approximations arose repeatedly during this century under various names
(Hecke algebras, centralizer rings, association schemes, coherent
configurations, cellular rings, etc.-see the first paper of the
collection for details) andin various branches of mathematics, both pure
and applied. One of these approximations, the theory of cellular rings
(cellular algebras), was developed at the end of the 60s by B. Yu.
Weisfeiler and A.A. Leman in the course of the first serious attempt to
study the complexity of the graph isomorphism problem, one of the
central problems in the modern theory of combinatorial algorithms. At
roughly the same time G.M. Adelson-Velskir, V.L. Arlazarov, I.A.
Faradtev and their colleagues had developed a rather efficient tool for
the constructive enumeration of combinatorial objects based on the
branch and bound method. By means of this tool a number of "sports-like"
results were obtained. Some of these results are still unsurpassed.