On 9 Dec 2014, pfd@pfdstudio.com wrote:

> For me, Summary only shows the unread messages, and not even the rest
> of the threads they belong to (unless I type 'A T').

For me, I have Gnus set to see unread/ticked article and threads that
have unread and ticked articles. I have

   1. "gnus-fetch-old-headers" set to "some".
   2. "gnus-build-sparse-threads" set to "some".
   
It is much cleaner this way, since it is not cluttered with articles of
no interest. If I want to see old read one, I just use "/o".

>>> but I'd settle for seeing all of the threads containing any unread
>>> messages. As I understand it, gnus-fetch-old-headers is supposed to
>>> do that, but I haven't found a way to make it work, at least with
>>> Fastmail.fm IMAP.

I do use imap- a local Dovecot server.

> The 'l' command in mutt is not search, it's limit ... it limits the
> display to messages matching some criteria. Admittedly I haven't
> searched exhaustively for gnus features to mimic this, but I didn't
> see any obvious ones. Of course, as I said, since only unread messages
> show up in the Summary, this is not very useful in gnus.

In Gnus "/" is "limited to". It is very powerful:

   https://www.gnu.org/software/emacs/manual/html_node/gnus/Limiting.html