@article{CMH_1980__55_139842,
     author = {Felice Ronga},
     title = {Om multiple points of smooth immersions.},
     journal = {Commentarii mathematici Helvetici},
     pages = {521--527},
     publisher = {mathdoc},
     volume = {55},
     year = {1980},
     zbl = {0457.57013},
     url = {http://geodesic.mathdoc.fr/item/CMH_1980__55_139842/}
}