@article{GMJ_2002__9_4_50551,
     author = {Brown, R. and Moore, E.J. and Porter, T. and Wensley, C.D.},
     title = {Crossed complexes, and free crossed resolutions for amalgamated sums and {HNN-extensions} of groups.},
     journal = {Georgian mathematical journal},
     pages = {623--644},
     year = {2002},
     volume = {9},
     number = {4},
     zbl = {1030.55013},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/GMJ_2002__9_4_50551/}
}