anchor.diff:     ) OPEN_BRACE subterm_ps_po_stanza CLOSE_BRACE
   ;
   
  -subterm_ps_po_stanza
  -:
  -   (
  -      (
  -         FROM
  -         (
  -            from_t_ps_stanza
  -            | inactive_from_t_ps_stanza
  -            |
  -            (
  -               OPEN_BRACE from_t_ps_stanza_list CLOSE_BRACE
  -            )
  -         )
  -      )
  -      |
  -      (
  -         TO
  -         (
  -            inactive_to_t_ps_stanza
  -            |
  -            (
  -               OPEN_BRACE to_t_ps_stanza_list CLOSE_BRACE
  -            )
  -            | to_t_ps_stanza
  -         )
  -      )
  -      |
  -      (
  -         THEN
  -         (
  -            inactive_then_t_ps_stanza
  -            |
  -            (
  -               OPEN_BRACE then_t_ps_stanza_list CLOSE_BRACE
  -            )
  -            | then_t_ps_stanza
  -         )
  -      )
  -   )+
  -;
  -
  -from_t_ps_stanza_list
  -:
  -   (
  -      from_t_ps_stanza
  -      | inactive_from_t_ps_stanza
  -   )+
  -;
  -
  -inactive_from_t_ps_stanza
  -:
  -   INACTIVE COLON from_t_ps_stanza
  -;
  -
  -from_t_ps_stanza
  -:
  -   as_path_from_t_ps_stanza
  -   | community_from_t_ps_stanza
  -   | family_from_t_ps_stanza
  -   | interface_from_t_ps_stanza
  -   | neighbor_from_t_ps_stanza
  -   | origin_from_t_ps_stanza
  -   | prefix_list_from_t_ps_stanza
  -   | prefix_list_filter_from_t_ps_stanza
  -   | protocol_from_t_ps_stanza
  -   | rib_from_t_ps_stanza
  -   | route_filter_from_t_ps_stanza
  -   | source_address_filter_from_t_ps_stanza
  -   | tag_from_t_ps_stanza
  -;
  -
  -then_t_ps_stanza_list
  -:
  -   (
  -      inactive_then_t_ps_stanza
  -      | then_t_ps_stanza
  -   )+
  -;
  -
  -inactive_then_t_ps_stanza
  -:
  -   INACTIVE COLON then_t_ps_stanza
  -;
  -
   then_t_ps_stanza
   :
      accept_then_t_ps_stanza
  
positive.code:    | null_po_stanza
  ;
  
  as_path_po_stanza
  :
     AS_PATH
     (
        name = VARIABLE
     )
     (
        string_in_double_quotes
        | ARI_CHANGETHIS3
     ) SEMICOLON
  ;
  
  community_po_stanza
  :
     COMMUNITY name = VARIABLE MEMBERS community_literal_list SEMICOLON
  ;
  
  policy_statement_po_stanza
  
negative.code:    | null_then_t_ps_stanza
  ;
  
  then_t_ps_stanza_list
  :
     (
        inactive_then_t_ps_stanza
        | then_t_ps_stanza
     )+
  ;
  
  to_t_ps_stanza_list
  :
     (
  