@article{CMH_1981__56_139880,
     author = {Jonathan A. Hillman},
     title = {Aspherical four-manifolds and the centres of two-knot groups.},
     journal = {Commentarii mathematici Helvetici},
     pages = {465--473},
     publisher = {mathdoc},
     volume = {56},
     year = {1981},
     zbl = {0478.57016},
     url = {http://geodesic.mathdoc.fr/item/CMH_1981__56_139880/}
}