The Free Logical Unit Number routine releases a logical unit
    number allocated by LIB$GET_LUN to the pool of available numbers.
    LIB$FREE_LUN is the complement of LIB$GET_LUN.

    Format

      LIB$FREE_LUN  logical-unit-number

1  –  Returns

    OpenVMS usage:cond_value
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

2  –  Argument

 logical-unit-number

    OpenVMS usage:longword_signed
    type:         longword integer (signed)
    access:       read only
    mechanism:    by reference

    Logical unit number to be deallocated. The logical-unit-number
    argument is the address of a signed longword integer that
    contains this logical unit number, which is the value previously
    returned by LIB$GET_LUN.