The extensions of a group
Compositio Mathematica, Tome 5 (1938) , pp. 357-367.
@article{CM_1938__5__357_0,
     author = {Turing, A. M.},
     title = {The extensions of a group},
     journal = {Compositio Mathematica},
     pages = {357--367},
     publisher = {Johnson Reprint Corporation},
     volume = {5},
     year = {1938},
     zbl = {0018.39201},
     language = {en},
     url = {www.numdam.org/item/CM_1938__5__357_0/}
}
Turing, A. M. The extensions of a group. Compositio Mathematica, Tome 5 (1938) , pp. 357-367. http://www.numdam.org/item/CM_1938__5__357_0/