Elementary Invariants

Points(D) : IncGeom -> SetIndx
Elements(D) : IncGeom -> SetIndx
Given an incidence geometry D, return the set of elements of D. These elements are the points of the incidence graph of D.
Types(D) : IncGeom -> SetIndx
Given an incidence geometry D, return the set of types of D.
Types(C) : CosetGeom -> SetIndx
Given a coset geometry C, return the set of types of C.
Rank(D) : IncGeom -> RngIntElt
Given an incidence geometry D, return the rank of D, i.e. the cardinality of the set of types.
Rank(C) : CosetGeom -> RngIntElt
Given a coset geometry C, return the rank of C.
IncidenceGraph(D) : IncGeom -> GrphUnd, GrphVertSet, GrphEdgeSet
Given an incidence geometry D, return the incidence graph of D, its vertex set and its edge set.

We remark that this function is not implemented for coset geometries but we may convert a coset geometry into an incidence geometry using IncidenceGeometry and then compute its incidence graph.

Group(C) : CosetGeom -> GrpPerm
Given a coset geometry C, return the group from which C is constructed.
MaxParabolics(C) : CosetGeom -> SetIndx
MaximalParabolics(C) : CosetGeom -> SetIndx
Given a coset geometry C, return an indexed set containing the maximal parabolics of C.
MinParabolics(C) : CosetGeom -> SetIndx
MinimalParabolics(C) : CosetGeom -> SetIndx
Given a coset geometry C, return an indexed set containing the minimal parabolics of C.
Borel(C) : CosetGeom -> GrpPerm
BorelSubgroup(C) : CosetGeom -> GrpPerm
Given a coset geometry C, return the Borel subgroup of C, i.e. the intersection of all maximal parabolic subgroups of C.
Kernel(C) : CosetGeom -> GrpPerm
Given a coset geometry C, return a permutation group which is its kernel, i.e. the subgroup of the Borel subgroup of C that fixes all elements of the geometry C.
Kernels(C) : CosetGeom -> SeqEnum
Given a coset geometry C, return a sequence containing the i-kernel Ki of each maximal parabolic subgroup Gi of C. The i-kernel of the subgroup Gi is the subgroup consisting of all the elements of Gi that fix all the elements of the residue of Gi.
Quotient(C, K) : CosetGeom, GrpPerm -> CosetGeom
Given a coset geometry C = (G; (Gi)i∈I) and a permutation group K, return the coset geometry (G/K; (Gi/K)i∈I) provided that K is a normal subgroup of G and of all the maximal parabolic subgroups of C.

V2.28, 13 July 2023