@article{AM2_1980__20_182379,
     author = {C.S. Hartzman},
     title = {Separatrices and singular points.},
     journal = {Aequationes mathematicae},
     pages = {59--72},
     publisher = {mathdoc},
     volume = {20},
     year = {1980},
     zbl = {0477.34025},
     url = {http://geodesic.mathdoc.fr/item/AM2_1980__20_182379/}
}