Fritsch, R & Fritsch, G <br/><br/>
Four-color theorem  history, topological foundations, & idea of proof 
R. Fritsch & G. Fritsch 
 - New York  Springer  1998 
 - xiv  260 
<br/><br/><label>ISBN: </label>9780387984971 
<br/><br/><label>Dewey Class. No.: </label>2.08  / FRIT