               Example 9

       Grammar for Four Function Calculator
       ------------------------------------

    expression      ->  term r-expression
 
    r-expression    ->  epsilon
                        | add-term r-expression
                        | subtract-term r-expression
 
*   add-term        -> "+" term
 
*   subtract-term   -> "-" term
 
    term            ->  factor r-term
 
    r-term          ->  epsilon
                        | multiply-factor r_term
                        | divide-factor r_term
        
*   multiply-factor ->  "*" factor

*   divide-factor   ->  "/" factor
 
    factor          ->  "(" expression ")"
*                       | integer
