@article{ASNSP_2003_5_2_2_287_0,
     author = {Hardt, Robert and Rivi\`ere, Tristan},
     title = {Connecting topological {Hopf} singularities},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {287--344},
     publisher = {Scuola normale superiore},
     volume = {Ser. 5, 2},
     number = {2},
     year = {2003},
     mrnumber = {2005606},
     zbl = {1150.58004},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_2003_5_2_2_287_0/}
}