W. Barthold: (1) _Turkyestan v’Epokhu Mongolskavo Nashyestviya_, St.
Petersburg, 1898.
—— (2) _Zur Geschichte des Christenthums in Mittel-Asien bis zur
Mongolischen Eroberungen_, German trans. by R. Stübe, Tubingen and
Leipzig, 1901.
—— (3) See under Radloff.
—— (4) Articles in _Encyclopaedia of Islām_.