Lagrange multipliers and generalized differentiable functions in vector extremum problems

In this paper, we establish a necessary optimality condition for a nondifferentiable vector extremum problem which involves a generalized vector-valued Lagrangian function. Such a condition is stated for a wide class of functions, which embraces the differentiable ones and a subclass of locally Lipschitzian functions. The condition embodies the classic theorem of F. John in multiobjective optimization.This research was partially supported by the Ministry of Public Education, Rome, Italy.