@book {BrTop, author = "Brown, Ronald", title = "Topology: a geometric account of general topology, homotopy types, and the fundamental groupoid", publisher = "Ellis Horwood, Chichester", year = "1988", } @book {BrTopGpd, author = "Brown, Ronald", title = "Topology and groupoids", publisher = "www.groupoids.org, Deganwy", year = "2006", } @article {BrMoPoWe, 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 Math. J.", volume = "9", year = "2002", pages = "623-644", } @book {HiGpd, author = "Higgins, Philip", booktitle = "Categories and Groupoids", publisher = "Van Nostrand Reinhold, London", year = "1971", } @article {HiJLMS, author = "Higgins, Philip", title = "The fundamental groupoid of a graph of groups", journal = "J. London Math. Soc.", volume = "13", year = "1976", pages = "145-149", } @phdthesis{emma-thesis, author = "Moore, Emma", title = "Graphs of groups: word computations and free crossed resolutions", type = "Ph.{D}.~thesis", year = "2001", school = "University of Wales, Bangor", } @book {Serre, author = "Serre, J.", title = "Trees", publisher = "Springer-Verlag, Berlin", year = "1980", }