Budziszewski, J.
Cambridge University Press, 2020
eBooks
Artikel Jurnal
Alfredo Rimper
Universitas Indonesia, 2011
UI - Tesis Open
E. Sumaryono
Kanisius, 2002
Buku Teks SO
Robert Maynard Hutchins, editor in chief
Encyclopaedia Britannica, Inc., 1952
Buku Referensi