emerge --depclean -a

 * Depclean may break link level dependencies. Thus, it is
 * recommended to use a tool such as `revdep-rebuild` (from
 * app-portage/gentoolkit) in order to detect such breakage.
 *
 * Always study the list of packages to be cleaned for any obvious
 * mistakes. Packages that are part of the world set will always
 * be kept.  They can be manually added to this set with
 * `emerge --noreplace <atom>`.  Packages that are listed in
 * package.provided (see portage(5)) will be removed by
 * depclean, even if they are part of the world set.
 *
 * As a safety measure, depclean will not remove any packages
 * unless *all* required dependencies have been resolved.  As a
 * consequence, it is often necessary to run `emerge --update
 * --newuse --deep @world` prior to depclean.

Calculating dependencies... done!
>>> Calculating removal order...

>>> These are the packages that would be unmerged:


!!! 'app-editors/nano' (virtual/editor) is part of your system profile.
!!! Unmerging it may be damaging to your system.


 app-editors/nano
    selected: 2.2.5
   protected: none
     omitted: none

 dev-lang/nasm
    selected: 2.09.10
   protected: none
     omitted: none

 sys-kernel/gentoo-sources
    selected: 3.2.1-r2
   protected: none
     omitted: 3.2.12

All selected packages: dev-lang/nasm-2.09.10 sys-kernel/gentoo-sources-3.2.1-r2 app-editors/nano-2.2.5

>>> 'Selected' packages are slated for removal.
>>> 'Protected' and 'omitted' packages will not be removed.

Would you like to unmerge these packages? [Yes/No]