1. R. Courant and H. Robbins, What Is Mathematics?, New York, 1941, pp. 354–358.
2. Alfred Weber, Über den Standort der Industrien, TÜbingen, 1909; Ch. III. The work has been translated as Alfred Weber's
Theory of the Location of Industries, Chicago, 1929, by C. J. Friedrich.
3. H. Steinhaus, Mathematical Snapshots, New York, 1960, p. 119. The use of this physical model was suggested by Georg Pick in his Mathematical Appendix to Weber's book, and the essential idea can be found in more modern treatments of force systems. See, for example, G. Polya, Induction and Analogy in Mathematics, Princeton 1954, pp. 147–148, and W. Miehle, “Link-Length Minimization in Networks, ” Operations Research, 6(1958), pp. 232–243.
4. Jean A, Ville, “Sur théorie géneral des jeux ou intervient l'ha-bilité des jouers ” Applications aux Jeux de Hasard by Emilie Borel and Jean Ville, Tome IV, Fasicule II, in the Traité du Calcul des Probabilités et de ses Applications by Emile Borel (1938), 105–113.
5. Harold W, Kuhn and A. W. Tucker, “Nonlinear Programming” in Proc. Second Berkeley Symposium on Mathematical Statistics and Probability, Univ. of Calif. Press, Berkeley, 1951, pp. 481–492.