@article{PM_1997_1997_1_a6,
     author = {Fran\c{c}oise, Jean-Pierre},
     title = {La primera derivada de la funci\'on del per{\'\i}odo de un campo vectorial plano.},
     journal = {Publicacions matem\`atiques},
     pages = {127-134},
     publisher = {mathdoc},
     volume = {41},
     number = {1},
     year = {1997},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PM_1997_1997_1_a6/}
}