old_contents: """Provide the SubmissionListingMixin class."""
  from ....const import API_PATH
  from ..generator import ListingGenerator
  from .base import BaseListingMixin
  from .gilded import GildedListingMixin
  
  
  class SubmissionListingMixin(BaseListingMixin, GildedListingMixin):
      """Adds additional methods pertaining to Submission instances."""
  
      def duplicates(self, **generator_kwargs):
          """Return a ListingGenerator for the submission's duplicates.
  
          Additional keyword arguments are passed in the initialization of
          :class:`.ListingGenerator`.
  
          """
          url = API_PATH['duplicates'].format(submission_id=self.id)
          return ListingGenerator(self._reddit, url, **generator_kwargs)
  
new_contents: """Provide the SubmissionListingMixin class."""
  from ....const import API_PATH
  from ..generator import ListingGenerator
  from .gilded import GildedListingMixin
  
  
  class SubmissionListingMixin(GildedListingMixin):
      """Adds additional methods pertaining to Submission instances."""
  
      def duplicates(self, **generator_kwargs):
          """Return a ListingGenerator for the submission's duplicates.
  
          Additional keyword arguments are passed in the initialization of
          :class:`.ListingGenerator`.
  
          """
          url = API_PATH['duplicates'].format(submission_id=self.id)
          return ListingGenerator(self._reddit, url, **generator_kwargs)
  
subject: Remove BaseListingMixin as superclass for SubmissionListingMixin