Second order equations of elliptic and parabolic type  
Landis, E. M. 
 - Providence, R.I. :  American Mathematical Society,  1998 
 - xii, 203 p. :  ill. ;  26 cm. 
 - Translations of mathematical monographs,  v. 171 .
<br/><br/><label>ISBN: </label>0821808575 (acid-free paper)