@article{MZ_1967__102_170881,
     author = {K.W. Gruenberg},
     title = {A {New} {Treatment} of {Group} {Extensions.}},
     journal = {Mathematische Zeitschrift},
     pages = {340--350},
     publisher = {mathdoc},
     volume = {102},
     year = {1967},
     zbl = {0178.01704},
     url = {http://geodesic.mathdoc.fr/item/MZ_1967__102_170881/}
}