1. E. Bishop and R. R. Phelps, A proof that every Banach space is subreflexive, American Mathematical Society. Bulletin 67 (1961), 97–98.
2. E. Bishop and R. R. Phelps, The support functionals of a convex set, in Proceedings of Symposiain Pure Mathematics, Vol. 7, American Mathematical Society, Providence, RI, 1963, pp. 27–35.
3. Lecture Notes in Mathematics;R. Bourgin,1983
4. F. S. De Blasi and G. Pianigiani, Remarks on Hausdorff continuous multifunction and selections, Commentationes Mathematicae Universitatis Carolinae 24 (1983), 553–561.
5. P. G. Georgiev, Parametric Ekeland’s variational principle, Applied Mathematics Letters 14 (2001), 691–696.