docs: def ngram_diff(args, parser):
      """Outputs the results of performing a diff query."""
      store = utils.get_data_store(args)
      corpus = utils.get_corpus(args)
      catalogue = utils.get_catalogue(args)
      tokenizer = utils.get_tokenizer(args)
      store.validate(corpus, catalogue)
      if args.asymmetric:
          store.diff_asymmetric(catalogue, args.asymmetric, tokenizer,
                                sys.stdout)
      else:
          store.diff(catalogue, tokenizer, sys.stdout)