PointGroup( G )
extracts the point group P of a space group G, binds it to
G.pointGroup, and returns it. It also determines the homomorphism from
G to P, and binds it to G.pointHomom. A point group P has always
a component P.isPointGroup set to true, and a component
P.crystGroup containing the CrystGroup from which it was constructed.
GAP 3.4.4