Except for the LBR$OUTPUT_HELP routine, you must call LBR$INI_
    CONTROL before calling any other LBR routine. After you
    initialize the library control index, you must open the library
    or create a new one using the LBR$OPEN routine. You can then call
    other LBR routines that you need. After you finish working with a
    library, close it with the LBR$CLOSE routine.

    LBR$INI_CONTROL initializes a library by filling the longword
    referenced by the library_index argument with the control index
    of the library. Upon completion of the call, the index can be
    used to refer to the current library in all future routine calls.
    Therefore, your program must not alter this value.

    You can have up to 16 libraries open simultaneously in your
    program.