The role of regularity to reach the vector valued version of Caristi's   fixed point theorem
  In this paper we discuss on the vector valued version of Caristi's theorem. We show that the regularity of the cone is an essential condition to reach the vector valued version of Caristi's theorem in vector valued metric spaces. It is shown that how the absence of the regularity causes some previous Caristi type theorems and results fail to be correct. Our main result give a vector valued version of Caristi's theorem for correspondences with weakened hypotheses in comparison with previous results and generalize them. 
Fatemeh Lael, Kourosh Nourouzi
math.FA