Coset Geometries

New Features:

• Some functions have been added to access the parabolic subgroups of a coset geometry : Group(D) returns the group from which D is constructed, MinimalParabolics(D) or MinParabolics(D) returns an indexed set containing all the minimal parabolic subgroups of D.
• The function Diagram(C) computes the diagram of the coset geometry C. This algorithm is much faster than the one for incidence geometries since it uses lots of group theory machinery in the computation.
• The function IsGraph(C) permits to check if the coset geometry C is a graph.
• The function Graph(C) permits to convert the coset geometry C into an object of type Graph provided C is a rank two geometry such that all elements of one type are incident with exactly two elements of the other.
• The full kernel of the coset geometry D can be computed using the Kernel(D) function and the i-kernels of D using the Kernels(D) function.
• The function Quotient(D,K) returns the quotient of the coset geometry D by a subgroup K provided that K is a subgroup of the kernel of D.