anchor.diff:      ;
   
   expression
  -    : term  (SPACE* (ADD | MULTIPLY | SUBTRACT | DIVIDE) expression)*
  +    : term  (SPACE* (ADD | MULTIPLY | SUBTRACT | DIVIDE | INTDIVIDE | MODULO | EXPONENT) expression)*
       ;
   
   term
  
positive.code:     : '}'
      ;
  
  GT
      : '>'
      ;
  
negative.code: 
  condition
      : term
      | (term (NGT | NLT | LT | GT | EQUALS) term)
      ;
  
  identifier
  