VMS Help LBR Routines, LBR$SET_MOVE, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 library_index

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference
    Library control index returned by the LBR$INI_CONTROL routine.
    The library_index argument is the address of the longword that
    contains the index.