  IF (file_instance^.fap_control_information.fap_array = NIL) AND
        (layer_number = 0) THEN
    layer := ^file_instance^.fap_control_information.first_fap;
  ELSEIF (file_instance^.fap_control_information.fap_array <> NIL) AND
        (layer_number <= UPPERBOUND (file_instance^.fap_control_information.
        fap_array^)) THEN
    layer := ^file_instance^.fap_control_information.fap_array^ [layer_number];
  ELSE
    osp$set_status_abnormal (amc$access_method_id, ame$improper_layer_number,
          interface_name, bam_status);
  IFEND;

