Chow, S-N., et al <br/><br/>
Normal forms & bifurcation of planar vector fields 
S-N. Chow, et al 
 - Cambridge  Cambridge University Press  1994 
 - viii  472 
<br/><br/><label>ISBN: </label>9780521372268 
<br/><br/><label>Dewey Class. No.: </label>6.07+12.01  / CHOW