Thomas, Joseph
Philadelphia : J.B. Lippincott, 1915
Buku Referensi
Gramedia Pustaka Utama, 2005
Buku Teks
Blakeney, E.H.
J.M. Dent & Sons, 1952
Buku Referensi
Backman, Louise
Stockholm Almqvist & Wiksell International 1975
Buku Teks
Hartmann, Reinhard R.K.
Routledge, 1998
Buku Referensi