@article{CMH_1972__47_139503,
     author = {Beno Eckmann and Urs Stammbach and Peter J. Hilton},
     title = {On the {Homology} {Theory} of {Central} {Group} {Extensions:} {I} - {The} {Commutator} {Map} and {Stem} {Extensions}},
     journal = {Commentarii mathematici Helvetici},
     pages = {102--122},
     publisher = {mathdoc},
     volume = {47},
     year = {1972},
     zbl = {0236.20038},
     url = {http://geodesic.mathdoc.fr/item/CMH_1972__47_139503/}
}