The command FpGroup will create a finitely presented group from an AgGroup.
The result has an entry .relators, that contains the relators of the
underlying Ag presentation. (The routine basically recomputes the
presentation by decomposing products and powers in the CGS).
If the ag group <G> is a parent with canonical generating system (this
is the case if you are using 'AgGroupFpGroup') then 'FpGroup(<G>)'
will construct the power-commutator presentation without collection.
So, "recomputes" is slightly misleading in this case.