@article{MM2_1980__32_154722,
     author = {Jose I. Nieto},
     title = {On the {Spherical} {Spectrum.}},
     journal = {Manuscripta mathematica},
     pages = {137--148},
     publisher = {mathdoc},
     volume = {32},
     year = {1980},
     zbl = {0455.47021},
     url = {http://geodesic.mathdoc.fr/item/MM2_1980__32_154722/}
}