Browning, Robert 1914-1997.
Byzantium and Bulgaria: a comparative study across the early medieval frontier /
Robert Browning 
. - Berkeley : Los Angeles : University of California Press,  1975 
. - 232 p.  map.  22 cm. 
<br/>К.: Бібліогр. : c. 207-210 
<br/><label>  ISBN: </label>0-520-02670-5