Lastrucci, Carlo L.
Schenkman, 1964
Buku Teks
Gauch, Hugh G., 1942-, author
Cambridge University Press, 2012
Buku Teks
Popper, Karl R., author
Basic Books, 1959
Buku Teks
Gower, Barry
Routledge, 1997
Buku Teks
Morris, Richard, author
Simon and Schuster, 1983
Buku Referensi