Ringel Gerhard <br/><br/>
Map Color Therorem 
/ by Gerhard Ringel 
 - New York  Springer Verlag  1974 
 - 191p. 
<br/><br/><label>ISBN: </label>3540065482 
<br/><br/><label>Dewey Class. No.: </label>511.5  / RIN/M