VMS Help DIFFERENCES, Parameters  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 input1-filespec

    Specifies the first file to be compared. The file specification
    must include a file name and a file type. The asterisk (*)  and
    the percent sign (%)  wildcard characters are not allowed.

 input2-filespec

    Specifies the second file to be compared. Unspecified fields
    default to the corresponding fields in the input1-filespec
    parameter. The asterisk (*)  and the percent sign (%) wildcard
    characters are not allowed.

    If you do not specify a secondary input file, the DIFFERENCES
    command uses the next lower version of the primary input file.