code: private Collection<Tuple> getCombinedTuples( List<VarDef> combinedVars, Collection<Tuple> tuples)
      {
      // Apply any once-only constraints.
      Set<Tuple> onceTuples = getOnceTupleDefs( combinedVars);
      if( !onceTuples.isEmpty())
        {
        for( Tuple tuple : tuples)
          {
          tuple.setOnce( onceTuples.contains( tuple));
          }
        }
      
      return tuples;
      }
docs: Returns all fully-combined N-tuples of values for the included input variables.