Ovsiannikov, L. <br/><br/>
Group analysis of differential equations / 
L. Ovsiannikov. 
 - [S.l.] :  Academic Pr,  1978. 
 - 432 p. 
<br/><br/><label>ISBN: </label>0125316801 9780125316804 
<br/><br/><label>Dewey Class. No.: </label>515.35