@article{10_4153_CJM_1980_036_7,
     author = {Roggenkamp, K. W.},
     title = {Groupings of {Metabelian} {Groups} and {Extension} {Categories}},
     journal = {Canadian journal of mathematics},
     pages = {449--459},
     year = {1980},
     volume = {32},
     number = {2},
     doi = {10.4153/CJM-1980-036-7},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1980-036-7/}
}