An incidence of a graph G is a pair (u, e) where u is a vertex of G and e is an edge of G incident with u. Two incidences (u, e) and (v, f ) of G are adjacent whenever (i) u = v, or (ii) e = f , or (iii) uv = e or uv = f . An incidence k-coloring of G is a mapping from the set of incidences of G to a set of k colors such that every two adjacent incidences receive distinct colors. The notion of incidence coloring has been introduced by Brualdi and Quinn Massey (1993) from a relation to strong edge coloring, and since then, attracted by many authors.On a list version of incidence coloring, it was shown by Benmedjdoub et. al. (2017) that every Hamiltonian cubic graph is incidence 6-choosable. In this paper, we show that every cubic (loopless) multigraph is incidence 6-choosable. As a direct consequence, it implies that the list strong chromatic index of a (2, 3)-bipartite graph is at most 6, where a (2,3)-bipartite graph is a bipartite graph such that one partite set has maximum degree at most 2 and the other partite set has maximum degree at most 3. *

In this article, we give spectra and characteristic polynomial of three partite complete graphs. We also give spectra of cartesian and tenor product of Kn,n,n with itself.Finally, we give general closed forms of the characteristic polynomials of the graphs obtained by identifying two copies of Kn at a vertex and an edge.

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