  Langrange duality theorems for vector and set optimization problems which are
based on an consequent usage of infimum and supremum (in the sense greatest
lower and least upper bounds with respect to a partial ordering) have been
recently proven. In this note, we provide an alternative proof of strong
duality for such problems via suitable stability and subdifferetial notions. In
contrast to most of the related results in the literature, the space of dual
variables is the same as in the scalar case, i.e., a dual variable is a vector
rather than an operator. We point out that duality with operators is an easy
consequence of duality with vectors as dual variables.
