Elen, L. W. F. Differential equations p-11 / L. W. F. Elen - London : Macmllan & Co LTD. c1967. - viii,,250 p. : ill. ; 22 cm. Includes index. english LCCN: 56005113 Subjects--Topical Terms: Differential equations. LC Class. No.: QA372 / .R4 1956 Dewey Class. No.: 517.38/ELD