Young, Jeffrey E.
Guilford Press, 2003
Buku Teks SO
Harsoyo
Majalah Mingguan Berita Pajak , 1974
Buku Teks
Verstegen, Judicus
Querido, 1970
Buku Teks
Merli, Mauro
Qe, 2013
Buku Teks SO
edited by Robert A. Brown and Joan Roberts Field
PMA Publishing, 1988
Buku Teks SO