public Vector<Identifier> getMultiKey(Identifier identifier) {
            Vector<Identifier> hash = new Vector<Identifier>();
            Vector<Identifier> one = new Vector<Identifier>();
            one.add(identifier);
            for (Entry<Identifier, HashSet<Vector<Identifier> > > ii : rules.entrySet() ){
                for (Vector<Identifier> i : ii.getValue()) {
                    if (i.equals(one)){
                        hash.add(ii.getKey());
                    }
                }
            }
            
            return hash;
        }