Hellwig G. <br/><br/>
Differential Operators of Mathematical Physics. An Untroduction 
Hellwig G. 
 - Reading etc.  Addison-Wesley Publishing Comp.  1964 
 - 296 p. 
<br/><br/> Translated from German by Hellwig B.,Fil kand 
<br/><br/><label>Dewey Class. No.: </label>517.983