@article{CMH_1981__56_139885,
     author = {Robert Brooks},
     title = {The fundamental group and the spectrum of the {Laplacian.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {581--598},
     publisher = {mathdoc},
     volume = {56},
     year = {1981},
     zbl = {0495.58029},
     url = {http://geodesic.mathdoc.fr/item/CMH_1981__56_139885/}
}