@inbook{CIF_1993-1994__22__38_0, author = {Colin de Verdi\`ere, Yves}, title = {Chapitre 3 {Multiplicit\'es} des valeurs propres}, booktitle = {Spectres de graphes}, series = {Cours de l'institut Fourier}, pages = {38--61}, publisher = {Institut des Math\'ematiques Pures - Universit\'e Scientifique et M\'edicale de Grenoble}, number = {22}, year = {1993-1994}, url = {http://archive.numdam.org/item/CIF_1993-1994__22__38_0/} }