@article{JAC_2001__14_1_a1,
     author = {\v{S}ir\'a\v{n}, Jozef},
     title = {Coverings of graphs and maps, orthogonality, and eigenvectors},
     journal = {Journal of Algebraic Combinatorics},
     pages = {57--72},
     publisher = {mathdoc},
     volume = {14},
     number = {1},
     year = {2001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JAC_2001__14_1_a1/}
}