@article{CMH_1972__47_139506,
     author = {Beno Eckmann and Urs Stammbach and Peter J. Hilton},
     title = {On the {Homology} {Theory} of {Central} {Group} {Extensions} {II.} {The} {Exact} {Sequence} in the {General} {Case}},
     journal = {Commentarii mathematici Helvetici},
     pages = {171--178},
     publisher = {mathdoc},
     volume = {47},
     year = {1972},
     zbl = {0246.20041},
     url = {http://geodesic.mathdoc.fr/item/CMH_1972__47_139506/}
}