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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_following(user, obj, flag=''):
 """ Checks if a "follow" relationship exists. Returns True if exists, False otherwise. Pass a string value to ``flag`` to determine which type of "follow" relationship you want to check. Example:: is_following(request.user, group) is_following(request.user, group, flag='liking') """

    check(obj)

    qs = apps.get_model('actstream', 'follow').objects.filter(
        user=user, object_id=obj.pk,
        content_type=ContentType.objects.get_for_model(obj)
    )

    if flag:
        qs = qs.filter(flag=flag)

    return qs.exists()