docs: public DBID findPrototype(DBIDs members) {
      // Find the last merge within the cluster.
      // The object with maximum priority will merge outside of the cluster,
      // So we need the second largest priority.
      DBIDIter it = members.iter();
      DBIDVar proto = DBIDUtil.newVar(it), last = DBIDUtil.newVar(it);
      int maxprio = Integer.MIN_VALUE, secprio = Integer.MIN_VALUE;
      for(; it.valid(); it.advance()) {
        int prio = mergeOrder.intValue(it);
        if(prio > maxprio) {
          secprio = maxprio;
          proto.set(last);
          maxprio = prio;
          last.set(it);
        }
        else if(prio > secprio) {
          secprio = prio;
          proto.set(it);
        }
      }
      return DBIDUtil.deref(prototypes.assignVar(proto, proto));
    }