@article{MZ_1968__107_171063,
     author = {R.B., Jr. Warfield},
     title = {Homomorphisms and {Duality} for {Torsion-free} {Groups.}},
     journal = {Mathematische Zeitschrift},
     pages = {189--200},
     publisher = {mathdoc},
     volume = {107},
     year = {1968},
     zbl = {0169.03602},
     url = {http://geodesic.mathdoc.fr/item/MZ_1968__107_171063/}
}