spectra of graphs; squares of graphs; bipartite graphs; metrically regular graphs (MRG); association scheme
Metrically regular bigraphs the square of which are metrically regular graphs are investigated in the case of graphs with 6 distinct eigenvalues (these eigenvalues can have variuos multiplicities).
 Vetchý V.: Metrically regular square of metrically regular bigraphs I
. Arch. Math. (Brno), Tomus 27b (1992), 183-197. MR 1189214