Guba V. <br/><br/>
Diagram Groups. 
Guba V., Sapir M. 
 - Providence  Amer. Math. Soc.  1997 
 - 125 p. 
<br/><br/> Memoirs of the Amer. Math. Soc., Vol. 130, N 620 
<br/><br/><label>Dewey Class. No.: </label>MAMS