code: def minus(repo_list_a, repo_list_b):
          included = defaultdict(lambda: False)
          for repo in repo_list_b:
              included[repo.full_name] = True
          a_minus_b = list()
          for repo in repo_list_a:
              if not included[repo.full_name]:
                  included[repo.full_name] = True
                  a_minus_b.append(repo)
          return a_minus_b