Western Press Agency, 1962
Buku Teks
Turnip, Sherly Saragih, author
Fakultas Psikologi Universitas Indonesia, 2010
Artikel Jurnal
Antoinette Schapper, author
University of Indonesia, Faculty of Humanities, 2011
Artikel Jurnal
Richards, Henry Erle, authors
Clarendon Press , 1915
Buku Teks
The University of Michigan Press , 1974
Buku Teks