De Zoete, Beryl
Faber and Faber Limited, 1957
Buku Teks
Endicott, Kirk Michael
Clarendon Press, 1970
Buku Teks
McGarry, Richard
John Wiley & Sons, 1992
Buku Teks
Loomis, C. Grant
The Mediaeval Academy of America, 1948
Buku Teks
Willmore, Job, author
American Society for Training & Development, 2009
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