Crossed complexes, and free crossed resolutions for amalgamated sums and HNN-extensions of groups. Brown, R.; Moore, E.J.; Porter, T.; Wensley, C.D. — 2002 Georgian Mathematical Journal
Graphs of morphisms of graphs. Brown, R.; Morris, I.; Shrimpton, J.; Wensley, C.D. — 2008 The Electronic Journal of Combinatorics [electronic only]