Silalahi, Udin
Badan Penerbit FHUI, 2019
Artikel Jurnal
Whish, Richard
Oxford University Press, 2018
Buku Teks
Dabbah, Maher M.
Cambridge University Press, 2007
Buku Teks SO
Edwards, Corwin D.
Press of Western Reserve University, 1956
Buku Teks
Goyder, Joanna
Oxford Univesity Press, 2009
Buku Teks