@article{AFM_1971_471-500_a5,
     author = {Seppo Heikkil\"a},
     title = {On the complete integrability of the first order total differential equation},
     journal = {Annales Fennici Mathematici},
     publisher = {mathdoc},
     volume = {471-500},
     year = {1971},
     doi = {10.5186/aasfm.1971.495},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.5186/aasfm.1971.495/}
}