def METHOD_NAME(parent_model, model, form):
    """
    Returns an inline form set where exactly one form must
    be in the formset.
    This is a bit weird since formsets are traditionally intended
    to contain any number of forms; however, for now it's the
    easiest way to shoehorn "sub-forms" into our form
    infrastructure without having to overhaul it.
    """
    return inlineformset_factory(
        parent_model,
        model,
        form,
        can_delete=False,
        min_num=1,
        max_num=1,
        validate_min=True,
        validate_max=True,
    )