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  [33m[B88]  [0m[1m[31mBrown,  R.  [0m,  [34mTopology: a geometric account of general topology,
  homotopy  types, and the fundamental groupoid[0m, Ellis Horwood, Chichester
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  [33m[B06]  [0m[1m[31mBrown,  R.  [0m,  [34mTopology and groupoids[0m, www.groupoids.org, Deganwy
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  [33m[BM+02] [0m[1m[31mBrown, R. and Moore, E. and Porter, T. and Wensley, C. [0m, [34mCrossed
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  HNN-extensions of groups[0m, Georgian Math. J., [34m9[0m (2002), 623-644
  
  [33m[H76]  [0m[1m[31mHiggins,  P.  [0m, [34mThe fundamental groupoid of a graph of groups[0m, J.
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  [33m[M01]  [0m[1m[31mMoore,  E. [0m, [34mGraphs of groups: word computations and free crossed
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  [33m[S80] [0m[1m[31mSerre, J. [0m, [34mTrees[0m, Springer-Verlag, Berlin (1980)
  
  
  
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