The line graph of the complete bipartite graph on sets with m and n vertices, denoted by L (Bmn), is the graph with mn vertices given by all ordered pairs (i, j), 1 ≤ i ≤ m, 1 ≤ j ≤ n.

Annals of Mathematics, SECOND SERIES, Vol. 182, No. 1 (July, 2015), pp. 307-325 (19 pages) We prove that there exist infinite families of regular bipartite Ramanujan graphs of every degree bigger than ...