@article{CMH_1988__63_4_140138,
     author = {Jonathan A. Hillman},
     title = {Two-knot groups with torsion free abelian normal subgroups of rank two.},
     journal = {Commentarii mathematici Helvetici},
     pages = {664--671},
     publisher = {mathdoc},
     volume = {63},
     number = {4},
     year = {1988},
     zbl = {0666.57016},
     url = {http://geodesic.mathdoc.fr/item/CMH_1988__63_4_140138/}
}