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
docs: Method to create a list of repositories such that the repository
          belongs to repo list a but not repo list b.
  
          In an ideal scenario we should be able to do this by set(a) - set(b)
          but as GithubRepositories have shown that set() on them is not reliable
          resort to this until it is all sorted out.
  
          :param repo_list_a: List of repositories.
          :param repo_list_b: List of repositories.