@article{PIM_1985_N_S_38_52_a5,
     author = {Mieczyslaw Borowiecki},
     title = {On {Spectrum} and {Per-spectrum} of {Graphs}},
     journal = {Publications de l'Institut Math\'ematique},
     pages = {31 },
     publisher = {mathdoc},
     volume = {_N_S_38},
     number = {52},
     year = {1985},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PIM_1985_N_S_38_52_a5/}
}