@article{TAC_1996_2_a0,
     author = {Ronald Brown and Christopher D. Wensley},
     title = {Computing crossed modules induced by an inclusion of a normal subgroup, 
with applications to homotopy 2-types},
     journal = {Theory and applications of categories},
     pages = {3--16},
     publisher = {mathdoc},
     volume = {2},
     year = {1996},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/TAC_1996_2_a0/}
}