Gelfand, I M. <br/><br/>
Calculus of Variations/ 
by I.M. Gelfand and S.V. Fomin. 
 - 1st. 
 - New York  Dover Publications Inc  2000 
 - 232p.  includes index;  21 cm. 
<br/><br/> 23-06-2022 
<br/><br/><label>ISBN: </label>0486414485