Erdos, Rene F. <br/><br/>
Teaching by correspondence / 
Rene F. Erdos 
 - London :  Longmans, Green & Co.,  1967 
 - 218 p. ;  20 cm. 
 - Unesco source book .
<br/><br/><label>Subjects--Topical Terms: </label><br/>Correspondence schools and courses