Bartholdi zeta functions of line graphs and middle graphs of graph coverings Original Research Article

We express the (Bartholdi type) L-functions of the line graph and the middle graph of a regular covering of a regular graph G by using some characteristic polynomials. As a corollary, we express the Bartholdi zeta functions of the line graph and the middle graph of a regular covering of G by using the characteristic polynomial of that regular covering.