Ore, Oystein  1899-1968. <br/><br/>
The four-color problem 

 - New York :  Academic Press,  1967 
 - xv, 259 p. :  il. 
 - Pure and applied mathematics. A series of monographs and textbooks  , 27 .
<br/><br/>p. 249-253 
<br/><br/><label>Subjects--Topical Terms: </label><br/>TEORIA DE GRAFOS
<br/><br/><label>Dewey Class. No.: </label>512.5  / O66f