1. Landau, E.: Grundlagen der Analysis. Leipzig 1930, or second American edition, New York 1948.
2. Cohen, L. W., and G. Ehrlich: The Structure of the Real Number System. Princeton-New York-Toronto-London 1963.
3. Dieudonné, J.: Foundations of Modern Analysis. New York-London 1960.
4. Dieudonné, J.: Calcul infinitésimal. Paris 1968, p. 41.
5. Mott, T. E.: On the quotient of monotone functions. Amer. Math. Monthly 70, 195–196 (1963).