“…The symmetric digraph D ( A ( G ) ) is obtained from G by replacing each edge of G by a symmetric pairzf arcs (a loop by a directed loop) and is denoted by 6. The bigraph B(G) is readily seen to be the graph K, x G, the Kronecker product [24] (also called tensor product [20] and conjunction [13]) of the graphs K, and G. Given a digraph D the underlying graph G ( D ) of D is the graph (possibly a multigraph) obtained by disregarding the orientation of the arcs in D. Thus each arc (vi, u j ) of D becomes an edge vivj of G ( D ) . In Figure 3 we show Lhe graph C, [the (undirectei) cycle, of length 41, the syrnmuetric digraph C,, the underlying graph G(C,) of C,, and the bigraph B(C,).…”