@article{1183552694, author = {Brooks, Robert}, title = {The first eigenvalue in a tower of coverings}, journal = {Bull. Amer. Math. Soc. (N.S.)}, volume = {12}, number = {1}, year = {1985}, pages = { 137-140}, language = {en}, url = {http://dml.mathdoc.fr/item/1183552694} }
Brooks, Robert. The first eigenvalue in a tower of coverings. Bull. Amer. Math. Soc. (N.S.), Tome 12 (1985) no. 1, pp. 137-140. http://gdmltest.u-ga.fr/item/1183552694/