Urwin, Kenneth
Hodder & Stoughton, 1968
Buku Referensi
edited by Marianne Chalmers and Martine Pierquin
Oxford University Press, 2002
Buku Referensi
HarperCollins, 2011
Buku Referensi
edited by Stephen Clarke
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Buku Referensi
Stimson, J. Frank, author
Martinus Nijhoff, 1964
Buku Referensi