1. Gunning, R. C. and Rossi, H. Analytic Functions of Several Complex Variables, Englewood Cliffs, N. J. 1965.
2. Hörmander, L. An Introduction to Complex Analysis in Several Variables, Toronto-New York-London 1966.
3. Robinson, A. Nonstandard Analysis, Studies in Logic and the Foundations of Mathematics, Amsterdam 1966.
4. _____. Germs, Applications of Model Theory to Algebra, Analysis, and Probability (ed. W. A. J. Luxemburg) New York, etc. 1969 pp. 138–149.