@incollection{AST_1992__210__115_0,
     author = {Hagedorn, George A.},
     title = {Classification and normal forms for quantum mechanical eigenvalue cossings},
     booktitle = {M\'ethodes semi-classiques Volume 2 - Colloque international (Nantes, juin 1991)},
     series = {Ast\'erisque},
     pages = {115--134},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {210},
     year = {1992},
     language = {en},
     url = {http://archive.numdam.org/item/AST_1992__210__115_0/}
}