1. R. G. Bartle, The Elements of Real Analysis, John Wiley, New York, 1964.
2. W. J. Baumol, Economic Theory and Operations Analysis, Prentice-Hall, Englewood Cliffs, NJ., 1972.
3. C. Berge, Topological Spaces, Macmillan, New York, 1963.
4. Normality and abnormality in the calculus of variations