Hofstadter, Richard
George Braziller, 1959
Buku Teks SO
Martin Brinkworth
Springer, 2012
eBooks
Rahner, Karl
The Crossroad Publishing Company, 1981
Buku Referensi
Doyglas J. Davies
Berg, 2002
Buku Teks SO
Descrates, Rene
J.M. Dent & Sons , 1949
Buku Teks SO