@article{MS2_1972__30_166237,
     author = {E. Thomas and L.L. Larmore},
     title = {Group {Extensions} and {Principal} {Fibrations.}},
     journal = {Mathematica Scandinavica},
     pages = {227--248},
     publisher = {mathdoc},
     volume = {30},
     year = {1972},
     zbl = {0254.55009},
     url = {http://geodesic.mathdoc.fr/item/MS2_1972__30_166237/}
}