1. Wolfe, P.: A Duality Theory for Nonlinear Programming. Quart. J. Appl. Math 19 (1961), 237–244.
2. Duffin, R. J.: Dual Programs and Minimum Cost. SIAM Jour. 10 (1962), 117–123.
3. Duffin, R. J.: Duality Inequalities of Mathematics and Science, in Nonlinear Programming, eds. Rosen, J. B., Mangasarian, O. L. and Ritter, K. New York: Academic Press, 1970, 401–423.
4. Mathematical Association of America, Studies in Mathematics;RJ Duffin,1975
5. Duffin, R. J.: Transformations that Aid Numerical Solution of Nonlinear Programs. Opsearch 18 (1981), 158–166.