APA

(1951). For the quarters October 1, 1950 - December 31, 1950, January 1, 1951 - March 31, 1951 and general survey from October 1,1949. Bonn: .

Chicago

1951. For the quarters October 1, 1950 - December 31, 1950, January 1, 1951 - March 31, 1951 and general survey from October 1,1949. Bonn: .

Harvard

(1951). For the quarters October 1, 1950 - December 31, 1950, January 1, 1951 - March 31, 1951 and general survey from October 1,1949. Bonn: .

MLA

For the quarters October 1, 1950 - December 31, 1950, January 1, 1951 - March 31, 1951 and general survey from October 1,1949. Bonn: . 1951.