Abstract. We study the duality problem for order weakly compact operators by giving sufficient and necessary conditions under which the order weak compactness of an operator implies the order weak compactness of its adjoint and conversely.2000 AMS Classification. 46A40; 46B40; 46B42. considered order weakly compact operators from a vector-valued function space into a Banach space and gave a characterization of an order weakly compact operator T in terms of the continuity of its adjoint relatively to some weak topologies.
Introduction and notation.Let us recall that an operator T from a Banach lattice E into a Banach space F is said to be order weakly compact if for each x ∈ E + , the subset T ([0, x]) is relatively weakly compact in F, where E + = {x ∈ E : 0 ≤ x}.Contrarily to weakly compact operators [2, 13], the class of order weakly compact operators satisfies the domination problem. Indeed, if S and T are two operators from a Banach lattice E into another F such that 0 ≤ S ≤ T and T is order weakly compact, then S is order weakly compact [3].Also, the class of order weakly compact operators does not satisfy the duality property, that is, there exist order weakly compact operators whose adjoints are not order weakly compact. In fact, the identity operator of the Banach lattice l 1 is order weakly compact, but its adjoint, which is the identity operator of the Banach lattice l ∞ , is not order weakly compact. And conversely, there exist operators that are not order weakly compact but their adjoints are order weakly compact. In fact, the identity operator of the Banach lattice l ∞ is not order weakly compact but its adjoint, which is the identity operator of the topological dual (l ∞ ) , is order weakly compact.In [16], Zaanen investigated the duality problem for semi-compact operators. Also, in [5] and [16], the duality problem of AM-compact operators on Banach lattices was studied. They gave sufficient and necessary conditions for which the AM-compactness