docs: def guess_home():
      '''If ``freesurfer_home`` is not set, try to make an intelligent guess at it'''
      global freesurfer_home
      if freesurfer_home != None:
          return True
      # if we already have it in the path, use that
      fv = nl.which('freeview')
      if fv:
          freesurfer_home = parpar_dir(os.path.realpath(fv))
          return True
      for guess_dir in guess_locations:
          if os.path.exists(guess_dir):
              freesurfer_home = guess_dir
              return True
      return False