Tangential Extremal Principles for Finite and Infinite Systems of Sets,   I: Basic Theory
  In this paper we develop new extremal principles in variational analysis that deal with finite and infinite systems of convex and nonconvex sets. The results obtained, unified under the name of tangential extremal principles, combine primal and dual approaches to the study of variational systems being in fact first extremal principles applied to infinite systems of sets. The first part of the paper concerns the basic theory of tangential extremal principles while the second part presents applications to problems of semi-infinite programming and multiobjective optimization. 
Boris S. Mordukhovich and Hung M. Phan
math.OC