/sys$common/syshlp/helplib.hlb LBR Routines, LBR$SET_INDEX, Arguments  *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.

 index_number

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference
    Index number you want to establish as the current index number.
    The index_number argument is the address of the longword that
    contains the number of the index you want to establish as the
    current index.