Returns a new set which is the intersection between this set and other.
That is, the returned set contains all the elements of this Set that
are also elements of other according to other.contains.
Source
Set<E> intersection(Set<Object> other) {
Set<E> result = toSet();
for (E element in this) {
if (!other.contains(element)) result.remove(element);
}
return result;
}