The  Keywords header content is one or more phrases intended
          to describe some aspect of the content of the article:

               Keywords-content = plain-phrase *( "," [ space ] plain-phrase )

          Keywords, separated  by  commas,  each  follow  the  <plain-
          phrase>  syntax  defined  in  section 5.2.  Encoded words in
          keywords MUST not contain characters other than letters  (of
          either case), digits, and the characters "!", "*", "+", "-",
          "/", "=", and "_".

               NOTE: Posters and posting agents are asked to take
               note that keywords are separated by commas, not by
               white space.  The following Keywords  header  con-
               tains  only  one  keyword  (a  rather unlikely and
               improbable one):

参考: 投稿者と投稿代理者はキーワードは空白間隔ではなしに 読点(コンマ)で区切ることに注意して下さい。次の Keywords 頭は キーワード1つだけ (ありそうもないですけど。) が含まれます。

                    Keywords: Thompson Ritchie Multics Linux

and should probably have been written:

おそらく次のように書くべきでした。

                    Keywords: Thompson, Ritchie, Multics, Linux

This particular error is unfortunately rather widespread.

残念なことにこの間違いは広く行われています。

               NOTE:   Reading  agents  and  archivers  preparing
               indexes of articles should bear in mind that user-
               chosen  keywords are notoriously poor for indexing
               purposes unless the keywords  are  picked  from  a
               predefined  set (which they are not in this case).
               Also, some followup agents unwisely propagate  the
               Keywords  header  from the precursor into the fol-
               lowup by default.  At least one news-based experi-
               ment has found the contents of Keywords headers to
               be completely valueless for indexing.