anchor.diff:     ;
   
   case_when_list
  -   : case_when_list case_when
  -   | case_when
  +   : case_when+
      ;
   
   case_when
  
positive.code:    ;
  
  frame_bound
     : UNBOUNDED PRECEDING
     | UNBOUNDED FOLLOWING
     | CURRENT_P ROW
     | a_expr PRECEDING
     | a_expr FOLLOWING
     ;
  
  opt_window_exclusion_clause
     : EXCLUDE CURRENT_P ROW
     | EXCLUDE GROUP_P
     | EXCLUDE TIES
     | EXCLUDE NO OTHERS
     |
     ;
  
  row
     : ROW OPEN_PAREN expr_list CLOSE_PAREN
     | ROW OPEN_PAREN CLOSE_PAREN
     | OPEN_PAREN expr_list COMMA a_expr CLOSE_PAREN
     ;
  
  
negative.code:    ;
  
  proc_exceptions
     : proc_exception+
     ;
  
  proc_exception
  