code: def paired_paths(main_path, fmt, formats):
      
      if not formats:
          return [(main_path, {'extension': os.path.splitext(main_path)[1]})]
  
      formats = long_form_multiple_formats(formats)
  
      # Is there a format that matches the main path?
      base = base_path(main_path, fmt)
      paths = [full_path(base, fmt) for fmt in formats]
  
      if main_path not in paths:
          raise InconsistentPath(u"Paired paths '{}' do not include the current notebook path '{}'. "
                                 u"Current format is '{}', and paired formats are '{}'."
                                 .format("','".join(paths), main_path, short_form_one_format(fmt),
                                         short_form_multiple_formats(formats)))
  
      if len(paths) > len(set(paths)):
          raise InconsistentPath(u'Duplicate paired paths for this notebook. Please fix jupytext.formats.')
  
      return list(zip(paths, formats))
docs: Return the list of paired notebooks, given main path, and the list of formats