code: public static <K,V> RelationFactory<K,V> mapSet() {
  	return mapSet(MapFacts.<K,Set<V>>hash(),
  		      SetFacts.<V>hash());
      }
docs: Returns a relation factory that generates
  <code>Relation</code>s interface backed by a
  <code>LinkedHashMap</code> from keys to
  <code>LinkedHashSet</code>s of values.  This relation factory
  is very good for programs that use only a few large relations.