Edmunds, D. E. and Evans, W. D. <br/><br/>
Spectral theory and differential operators   

 - Oxford  Clarendon Press  1989 
 - xvi, 574p. Index, Bibl. 
 - Oxford Mathematical monographs .
<br/><br/>  
<br/><br/><label>Dewey Class. No.: </label>515.72  / Ed24.ST