Hellwig, Gunter. <br/><br/>
Differential operators of mathematical physics  :an introduction 
/DUNTER HELLWIG 
 - Massachusetts  Addison-Wesley Pub.  1964 
 - vii, 296 p. 
<br/><br/> Includes bibliography, appendix, index 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Differential operators
<br/><br/><label>Dewey Class. No.: </label>515.72  / HEL