19. Coxeter diagrams and graphs of groups
  
      |  CoxeterDiagramComponents(D)  Inputs a Coxeter diagram D and returns a list [D_1, ..., D_d] of the maximal connected subgraphs D_i.                                                                                                                                                                                                          | 
      |  CoxeterDiagramDegree(D,v)  Inputs a Coxeter diagram D and vertex v. It returns the degree of v (i.e. the number of edges incident with v).                                                                                                                                                                                                  | 
      |  CoxeterDiagramDisplay(D)   CoxeterDiagramDisplay(D,"web browser")  Inputs a Coxeter diagram D and displays it as a .gif file. It uses the Mozilla web browser as a default to view the diagram. An alternative browser can be set using a second argument. This function requires Graphviz software.                                        | 
      |  CoxeterDiagramFpArtinGroup(D)  Inputs a Coxeter diagram D and returns the corresponding finitely presented Artin group.                                                                                                                                                                                                                     | 
      |  CoxeterDiagramFpCoxeterGroup(D)  Inputs a Coxeter diagram D and returns the corresponding finitely presented Coxeter group.                                                                                                                                                                                                                 | 
      |  CoxeterDiagramIsSpherical(D)  Inputs a Coxeter diagram D and returns "true" if the associated Coxeter groups is finite, and returns "false" otherwise.                                                                                                                                                                                      | 
      |  CoxeterDiagramMatrix(D)  Inputs a Coxeter diagram D and returns a matrix representation of it. The matrix is given as a function DiagramMatrix(D)(i,j) where i,j can range over the vertices.                                                                                                                                               | 
      |  CoxeterSubDiagram(D,V)  Inputs a Coxeter diagram D and a subset V of its vertices. It returns the full sub-diagram of D with vertex set V.                                                                                                                                                                                                  | 
      |  CoxeterDiagramVertices(D)  Inputs a Coxeter diagram D and returns its set of vertices.                                                                                                                                                                                                                                                      | 
      |  EvenSubgroup(G)  Inputs a group G and returns a subgroup G^+. The subgroup is that generated by all products xy where x and y range over the generating set for G stored by GAP. The subgroup is probably only meaningful when G is an Artin or Coxeter group.                                                                              | 
      |  GraphOfGroupsDisplay(D)   GraphOfGroupsDisplay(D,"web browser")  Inputs a graph of groups D and displays it as a .gif file. It uses the Mozilla web browser as a default to view the diagram. An alternative browser can be set using a second argument. This function requires Graphviz software.                                          | 
      |  GraphOfGroupsTest(D)  Inputs an object D and itries to test whether it is a Graph of Groups. However, it DOES NOT test the injectivity of any homomorphisms. It returns true if D passes the test, and false otherwise. Note that there is no function IsHapGraphOfGroups() because no special data type has been created for these graphs. |