- Use <Elements>.containsAll(Collection) instead of contains(Set). The latter does not check if all the <QueriedElements> in the Set are present, but if the Set itself is contained in <Elements>
 - Further: use correct order: <Elements>.containsAll(<QueriedElements>) and not vice-versa
- Use Sets to avoid duplicates in the return values of further methods. Introduce toEList() method for the conversion Set -> EList
refs 2950