There are two kind of intersection algorithms. Whenever the product of
two subgroups is a subgroup, a generalized Zassenhaus algorithm can be
used in order to compute the intersection and sum (see GS90). In
case one subgroup is a normalized by the other, an element of the sum can
easyly be decomposed. The functions IntersectionSumAgGroup (see
IntersectionSumAgGroup), NormalIntersection (see NormalIntersection
), SumFactorizationFunctionAgGroup (see
SumFactorizationFunctionAgGroup) and SumAgGroup (see SumAgGroup)
should be used in such cases.
These functions are faster than the general function Intersection (see
Intersection and Intersection for Ag Groups), which can compute the
intersection of two subgroups even if their product is no subgroup.
GAP 3.4.4