@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://www.numdam.org/item/CIF_1993-1994__22__38_0/}
}