code: public void setTupleSize( int tupleSize)
      {
      Integer onceSize =
        onceTuples_.isEmpty()
        ? null
        : getOnceTuples().next().size();
  
      if( !(onceSize == null || onceSize == tupleSize))
        {
        throw new IllegalArgumentException( "Tuple size=" + tupleSize + " is not compatible with existing once-only tuple size=" + onceSize);
        }
      
      tupleSize_ = tupleSize;
      }
docs: Changes the tuple size for input variable combinations. A non-positive tupleSize specifies
  all permutations.