1. R. Courant and H. Robbins, What is Mathematics? 4th ed., Oxford University Press, London, New York, Toronto, 1960.
2. B. W. Jones, Elementary Concepts of Mathematics, 2nd ed., Macmillan, New York, 1963.
3. M. L. Keedy, A Modern Introduction to Basic Mathematics, Addison-Wesley, Reading, Mass., 1963.
4. H. Rademacher and O. Toeplitz, The Enjoyment of Mathematics, Princeton University Press, 1957.