References
Charles A. Ferguson
(1978)., Historical background of universals research, in J. Greenberg (ed.), Universals of human language, Stanford, Stanford University Press, pp. 7-32.
with Greenberg, J. , Moravcsik, E.A. (eds) (1978). Universals of human language 4: syntax, Stanford University Press, Stanford.
(1959). Diglossia. Word 15, pp. 325-340.