1. S. Al-Homidan, Q.H. Ansari, J.-C. Yao, Some generalizations of Ekeland-type variational principle with applications to equilibrium problems and fixed point theory. Nonlinear Anal. 69(1), 126–139 (2008)
2. L. Altangerel, R.I. Bot, G. Wanka, Variational principles for vector equilibrium problems related to conjugate duality. J. Nonlinear Convex Anal. 8(2), 179–196 (2007)
3. Q.H. Ansari, Vector equilibrium problems and vector variational inequalities, in: Vector Variational Inequalities and Vector Equilibria. Mathematical Theories, ed. by F. Giannessi (Kluwer Academic, Dordrecht/Boston/London, 2000), pp. 1–15
4. Q.H. Ansari, Vectorial form of Ekeland-type variational principle with applications to vector equilibrium problems and fixed point theory. J. Math. Anal. Appl. 334, 561–575 (2007)
5. Q.H. Ansari, Metric Spaces – Including Fixed Point Theory and Set-Valued Maps (Narosa Publishing House, New Delhi, 2010). Also Published by Alpha Science International Ltd. Oxford, U.K. (2010)