<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def unread(thread, user):
 """ Check whether there are any unread messages for a particular thread for a user. """

    return bool(thread.userthread_set.filter(user=user, unread=True))