/sys$common/syshlp/helplib.hlb DEASSIGN, Qualifiers, /PROCESS  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /PROCESS (default)

    Indicates that the specified logical name is in the process
    logical name table. The /PROCESS qualifier is synonymous with
    the /TABLE=LNM$PROCESS qualifier.

    You cannot deassign logical name table entries that were made by
    the command interpreter, for example, SYS$INPUT, SYS$OUTPUT, and
    SYS$ERROR. However, if you assign new equivalence names for these
    logical names (that is, create new logical names in outer access
    modes), you can deassign the names you explicitly created.