Sharpe, Gareth, author
Guinness Publishing, 1994
Buku Referensi
Andy Ilman Hakim, author
2017
UI - Tesis (Membership)
Dowis, Richard, author
[American Management Association, ], 2000
eBooks
Greene, Richard
Red & White Pub., 2010
Buku Teks
Aaron, David, author
Citadel Press , [1961]
Buku Teks