code: def create_concept_scheme(rdf, ns, lname=''):
      
  
      ont = None
      if not ns:
          # see if there's an owl:Ontology and use that to determine namespace
          onts = list(rdf.subjects(RDF.type, OWL.Ontology))
          if len(onts) > 1:
              onts.sort()
              ont = onts[0]
              logging.warning(
                  "Multiple owl:Ontology instances found. "
                  "Creating concept scheme from %s.", ont)
          elif len(onts) == 1:
              ont = onts[0]
          else:
              ont = None
  
          if not ont:
              logging.info(
                  "No skos:ConceptScheme or owl:Ontology found. "
                  "Using namespace auto-detection for creating concept scheme.")
              ns = detect_namespace(rdf)
          elif ont.endswith('/') or ont.endswith('#') or ont.endswith(':'):
              ns = ont
          else:
              ns = ont + '/'
  
      NS = Namespace(ns)
      cs = NS[lname]
  
      rdf.add((cs, RDF.type, SKOS.ConceptScheme))
  
      if ont is not None:
          rdf.remove((ont, RDF.type, OWL.Ontology))
          # remove owl:imports declarations
          for o in rdf.objects(ont, OWL.imports):
              rdf.remove((ont, OWL.imports, o))
          # remove protege specific properties
          for p, o in rdf.predicate_objects(ont):
              prot = URIRef(
                  'http://protege.stanford.edu/plugins/owl/protege#')
              if p.startswith(prot):
                  rdf.remove((ont, p, o))
          # move remaining properties (dc:title etc.) of the owl:Ontology into
          # the skos:ConceptScheme
          replace_uri(rdf, ont, cs)
  
      return cs
docs: Create a skos:ConceptScheme in the model and return it.