//
/** a mapping from topologies over <tt>K</tt> to <i>sets of</i> values of type <tt>V</tt> */
-public class TopologicalBag<K,V> implements MapBag<Topology<K>,V>, VisitableMap<K,V> {
+public class TopologicalBag<K,V> implements MapBag<Topology<K>,V>, VisitableMap<K,V>, Serializable {
// CRUCIAL INVARIANT: keys in this hashmap MUST be disjoint or the universe will implode
private final HashMap<Topology<K>,HashSet<V>> h = new HashMap<Topology<K>,HashSet<V>>();