@Override
public Iterator<Entry<Integer, Double>> getNestedTransitionsIterator(int s, int i, int j) {
DistributionSet ds = trans.get(s).get(i);
Iterator<Distribution> iter = ds.iterator();
Distribution distr = null;
int k = 0;
while (iter.hasNext() && k <= j) {
distr = iter.next();
k++;
}
if (k <= j) return null;
else return distr.iterator();
}
