code: def skos_symmetric_mappings(rdf, related=True):
      
      for s, o in rdf.subject_objects(SKOS.relatedMatch):
          rdf.add((o, SKOS.relatedMatch, s))
          if related:
              rdf.add((s, SKOS.related, o))
              rdf.add((o, SKOS.related, s))
  
      for s, o in rdf.subject_objects(SKOS.closeMatch):
          rdf.add((o, SKOS.closeMatch, s))
  
      for s, o in rdf.subject_objects(SKOS.exactMatch):
          rdf.add((o, SKOS.exactMatch, s))
docs: Ensure that the symmetric mapping properties (skos:relatedMatch,
      skos:closeMatch and skos:exactMatch) are stated in both directions (S44).
  
      :param bool related: Add the skos:related super-property for all
          skos:relatedMatch relations (S41).