
gap/pcpgrp:

higher level functions for pcp groups:

fitting.gi    -- fitting subgroup, centre, FC-centre, etc.
pcpattr.gi    -- some general functions, not installed attributes
maxsub.gi     -- maximal subgroups
findex.gi     -- subgroups of finite index  (LowIndex)
nindex.gi     -- normal subgroups of finite index
polyz.gi      -- compute a poly-Z normal subgroup
grpinva.gi    -- invariant subspaces
torsion.gi    -- finite subgroups (TorsionSubgroup / FiniteSubgroups)

nilpot.gi     -- centralizers in nilpotent groups
inters.gi     -- intersection with normal subgroup
centnorm.gi   -- centralizers and normalizers 

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Centalizer
Normalizer
Intersection

A SemiSimpleEfaSeries (this is not unique for G!)
A FittingSubgroup
A Centre
A UpperCentralSeries 
A FCCentre
F NilpotentByAbelianByFiniteStructure
A IsNilpotentByFinite
A MinimalGeneratingSet
A MaximalSubgroupClassesByIndex
A SylowSubgroups
A LowIndexSubgroupClasses
A LowIndexNormalSubgroups
(F NilpotentByAbelianNormalSubgroup - application of LowIndexNormals)
F PolyZNormalSubgroup
A TorsionSubgroup 
A NormalTorsionSubgroup
P IsTorsionFree
A FiniteSubgroupClasses 
F RootSet

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Todo - Centralizer 
     - Normalizer
     - Intersection (check with inters.gi)
     - clear up general.gi
