PROCEDURE HILIGHT_BLOCK;
   EXTERNAL;
FUNCTION START_BLOCK : BOOLEAN;
   EXTERNAL;
FUNCTION END_BLOCK : BOOLEAN;
   EXTERNAL;
FUNCTION DESELECT_BLOCK : BOOLEAN;
   EXTERNAL;
PROCEDURE DELETE_BLOCK;
   EXTERNAL;
PROCEDURE SHIFT_BLOCK ( action,
                        dest_r,dest_c,      { definitions as above }
                        st_r,st_c,e_r,e_c  : INTEGER   );
   EXTERNAL;
FUNCTION TRANSPORT_BLOCK ( action : INTEGER ) : BOOLEAN;
   EXTERNAL;

PROCEDURE DISK_IO ( what : DiskIoOps );
   EXTERNAL;