Infinitary Axiomatizability of Slender and Cotorsion-Free Groups
arXiv:math/9910162
Abstract
The classes of slender and cotorsion-free abelian groups are axiomatizable in the infinitary logics L_{infty,omega_1} and L_{infty,omega}, respectively. The Baer-Specker group Z^omega is not L_{infty,omega_1}-equivalent to a slender group.