Ore, Oystein,  1899-1968 <br/><br/>
The four-color problem / 
Oystein Ore 
 - New York :  Academic Press,  1967 
 - 259 p. :  ill. ;  24 cm. 
 - Pure and applied mathematics  27 .
<br/><br/> Includes index 
<br/><br/>Bibliography:p.249-253 
<br/><br/><label>ISBN: </label>0125281501 
<br/><br/><label>LCCN: </label>66-30095 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Four--color problem