@article{FORUM_1994__6_3_141746,
     author = {Friedrich Hegenbarth and Alberto Cavicchioli},
     title = {On 4-manifolds with free fundamental group.},
     journal = {Forum mathematicum},
     pages = {415--430},
     publisher = {mathdoc},
     volume = {6},
     number = {3},
     year = {1994},
     zbl = {0822.57015},
     url = {http://geodesic.mathdoc.fr/item/FORUM_1994__6_3_141746/}
}