anchor.diff:   ;           
   
   pass_statement
  - : PASS
  + : Mark=PASS
    ;
   
   flow_statement
  
positive.code:  ;
  
  break_statement
   : BREAK
   ;
  
  return_statement
   : RETURN expression?
   ;
  
  compound_statement
  
negative.code: 
  bool_not_expression
   : comparison_expression
   | Op=NOT Right=bool_not_expression
   ;
  
  comparison_expression
  