@article{HHA_2002_4_1_a7,
     author = {D. Bourn and E. M. Vitale},
     title = {Extensions of symmetric cat-groups},
     journal = {Homology, homotopy, and applications},
     pages = {103--162},
     publisher = {mathdoc},
     volume = {4},
     number = {1},
     year = {2002},
     doi = {10.4310/HHA.2002.v4.n1.a8},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4310/HHA.2002.v4.n1.a8/}
}