Levi, Decio  <br/><br/>
Symmetries and integrability of difference equations/ 
Decio Levi, Peter Olver, Zora Thomova and Pavel Winternitz 
 - Cambridge:   Cambridge University Press,   c2011.  
 - xviii, 341 pages :   illustrations ;   23 cm. 
<br/><br/>Includes bibliographical references.<br/> 
<br/><br/><label>ISBN: </label>9780521136587 (pbk.)