@article{10_4064_cm_65_1_87,
     author = {Pierre de la Harpe and A. Robertson and Alain Valette},
     title = {On the spectrum of the sum of generators of a finitely generated group, {II}},
     journal = {Colloquium Mathematicum},
     pages = {87--87},
     publisher = {mathdoc},
     volume = {65},
     number = {1},
     year = {1993},
     doi = {10.4064/cm-65-1-87},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm-65-1-87/}
}