TranslationsCrystGroup( G )
determines a basis of the translation lattice of G, binds it to
G.translations, and returns it. Note that this translation lattice is
always invariant under the point group P of G. If G.translations
is not yet present, a finite presentation of P needs to be determined.
A basis of the translation lattice can also be added by the user, with
AddTranslationsCrystGroup (see AddTranslationsCrystGroup).
Warning: The component G.translations must never be set by hand.
The functions TranslationsCrystGroup and AddTranslationsCrystGroups
have important (and wanted) side effects.
GAP 3.4.4