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