Qualitative theory of planar differential systems 
Dumortier, Freddy. 
 - Berlin ; | New York :  Springer,  2006 
 - xvi, 298 p. :  ill. ;  24 cm. 
 - Universitext .
<br/><br/><label>ISBN: </label>9783540328933 (pbk.) | 3540328939 (pbk.)