def tag_slice_iter_from_slices_of_tag_dict(slices_of_tag):
    """
    Get an iterator of (tag, (bt, tt)) pairs
    :param slices_of_tag: a {tag: [(bt, tt),...], ...} dict listing slices annotated by tags
    :return: a tag, (bt, tt) iterator
    """
    for tag, slices in slices_of_tag.items():
        for sl in slices:
            yield tag, sl
