code: public void used( Tuple tuple)
      {
      // Currently unused?
      int i = unused_.indexOf( tuple);
      if( i >= 0)
        {
        // Yes, relocate to used list. 
        unused_.remove( i);
        addUsed( tuple);
  
        if( tuple.size() > 1)
          {
          // Once used, N-tuples can be reduced to 1-tuples.  This enables different combinations
          // that may be required to complete tests for other tuples. In particular, it allows for an
          // NA binding of an optional variable, which will never appear in N-tuples.
          for( Iterator<VarBindingDef> bindings = tuple.getBindings(); bindings.hasNext();)
            {
            Tuple tuple1 = new Tuple( bindings.next());
            tuple1.setOnce( tuple.isOnce());
  
            // 1-tuple already used?
            if( (i = used_.indexOf( tuple1)) >= 0)
              {
              // Yes, move to the end of the list. This acts to keep the used list
              // in least-recently-used-first order.
              used_.remove( i);
              }
            addUsed( tuple1);
            }
          }
        }
  
      // No, already used?
      else if( (i = used_.indexOf( tuple)) >= 0)
        {
        // Yes, move to the end of the list. This acts to keep the used list
        // in least-recently-used-first order.
        addUsed( used_.remove( i));
        }
      }
docs: Asserts that the given tuple has been used in a test case.