Combinatorial group theory : 
Magnus, Wilhelm, 
 - Mineola, N.Y. :  Dover Publications,  2004 
 - xii, 444 p. ; 22 cm. 
<br/><br/> Previously published: 2nd rev. ed. New York : Dover Publications, 1976. 
<br/><br/><label>ISBN: </label>0486438309 (pbk.)