Equilibrium problems provide a unifying framework for many important problems, such as optimization problems, variational inequality problems, complementarity problems, minimax inequality problems, and fixed point problems. They have been widely applied to study real word applications, arising in economics, mechanics, and engineering science. In recent decades, many results concerning the existence of solutions for equilibrium problems and vector equilibri-um problems have been established (see Ansari and Yao [1], Bianchi and Schaible [2], and Blum and Oettli [3]). Many problems of practical interest in optimization, economics, physics, mechanics, and engineering sciences involve equilibrium in their description. Because of their wide applicability, equilibrium problems and mixed equilibrium problems have been investigated and generalized by a number of authors
