@article{RCM_1973__7_181606,
     author = {Alberto Medina},
     title = {Une note sur les unvariants caract\'eristiques de certains ...},
     journal = {Revista colombiana de matematicas},
     pages = {109--112},
     year = {1973},
     volume = {7},
     zbl = {0273.57006},
     url = {http://geodesic.mathdoc.fr/item/RCM_1973__7_181606/}
}