E. Matouskova et C. Stegall, A CHARACTERIZATION OF REFLEXIVE BANACH-SPACES, Proceedings of the American Mathematical Society, 124(4), 1996, pp. 1083-1090
A Banach space Z is not reflexive if and only if there exist a closed
separable subspace X of Z and a convex closed subset Q of X with empty
interior which contains translates of all compact sets in X. If, more
over, Z is separable, then it is possible to put X = Z.