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#### 2.16.4 Topic Topology

So, let's have a look at an example group buffer:

         Gnus
           Emacs -- I wuw it!
              3: comp.emacs
              2: alt.religion.emacs
             Naughty Emacs
              452: alt.sex.emacs
                0: comp.talk.emacs.recovery
           Misc
              8: comp.binaries.fractals
             13: comp.sources.unix

So, here we have one top-level topic (‘`Gnus`’), two topics under that, and one sub-topic under one of the sub-topics. (There is always just one (1) top-level topic). This topology can be expressed as follows:

         (("Gnus" visible)
          (("Emacs -- I wuw it!" visible)
           (("Naughty Emacs" visible)))
          (("Misc" visible)))

This is in fact how the variable `gnus-topic-topology` would look for the display above. That variable is saved in the `.newsrc.eld` file, and shouldn't be messed with manually—unless you really want to. Since this variable is read from the `.newsrc.eld` file, setting it in any other startup files will have no effect.

This topology shows what topics are sub-topics of what topics (right), and which topics are visible. Two settings are currently allowed—`visible` and `invisible`.