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

 - Oxford  Clerendon press  1990 
 - (xviii), 5 
<br/><br/><label>ISBN: </label>0-19-853542-2 
<br/><br/><label>Dewey Class. No.: </label>515.7246