<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 async def verify_parent_task(chain, link):
 """Verify the parent task Link. Action task verification is currently in the same verification function as decision tasks, because sometimes we'll have an action task masquerading as a decision task, e.g. in templatized actions for release graphs. To make sure our guess of decision or action task isn't fatal, we call this function; this function uses ``is_action()`` to determine how to verify the task. Args: chain (ChainOfTrust):
 the chain we're operating on. link (LinkOfTrust):
 the task link we're checking. Raises: CoTError: on chain of trust verification error. """

    worker_type = get_worker_type(link.task)
    if worker_type not in chain.context.config['valid_decision_worker_types']:
        raise CoTError("{} is not a valid decision workerType!".format(worker_type))
    if chain is not link:
        # make sure all tasks generated from this parent task match the published
        # task-graph.json. Not applicable if this link is the ChainOfTrust object,
        # since this task won't have generated a task-graph.json yet.
        path = link.get_artifact_full_path('public/task-graph.json')
        if not os.path.exists(path):
            raise CoTError("{} {}: {} doesn't exist!".format(link.name, link.task_id, path))
        link.task_graph = load_json_or_yaml(
            path, is_path=True, exception=CoTError, message="Can't load {}! %(exc)s".format(path)
        )
        # This check may want to move to a per-task check?
        for target_link in chain.get_all_links_in_chain():
            # Verify the target's task is in the parent task's task graph, unless
            # it's this task or a parent task.
            # (Decision tasks will not exist in a parent task's task-graph.json;
            #  action tasks, which are generated later, will also be missing.)
            # https://github.com/mozilla-releng/scriptworker/issues/77
            if target_link.parent_task_id == link.task_id and \
                    target_link.task_id != link.task_id and \
                    target_link.task_type not in PARENT_TASK_TYPES:
                verify_link_in_task_graph(chain, link, target_link)
    try:
        await verify_parent_task_definition(chain, link)
    except (BaseDownloadError, KeyError) as e:
        raise CoTError(e)