Garden City Books, [date of publication not identified]
Buku Referensi
Debenham, Frank, author
Reader's Digest Association, 1979
Buku Referensi
edited by John A. Wolter and Ronald E. Grim
Library of Congress, 1977
Buku Referensi
Pergamon Press, 1968
Buku Referensi
edited by Martin Haspelmath, Matthew S. Dryer, David Gil and Bernard Comrie
Oxford University , 2005
Buku Referensi