Open Univeristy <br/><br/>
Planarity and colouring 

 -  1981 
 - p.  cm. 
<br/><br/><label>Standard No.: </label>23726 
<br/><br/><label>Source: </label> Textual 
<br/><br/><label>Dewey Class. No.: </label>B44, M1.12