@article{AIF_2003__53_4_1023_0,
     author = {Colin de Verdi\`ere, Yves},
     title = {The level crossing problem in semi-classical analysis {I.} {The} symmetric case},
     journal = {Annales de l'Institut Fourier},
     pages = {1023--1054},
     publisher = {Association des Annales de l{\textquoteright}institut Fourier},
     volume = {53},
     number = {4},
     year = {2003},
     doi = {10.5802/aif.1973},
     mrnumber = {2033509},
     zbl = {02014671},
     language = {en},
     url = {http://www.numdam.org/articles/10.5802/aif.1973/}
}