def _get_merging_map(a, b, b_name_pos: int = 7) -> dict:
    """Intersect BED files to obtain a dict with b names as keys and
       overlapped a names for each b in values as list
    """
    joined = a.intersect(b, wao=True)
    res = {x.name: [] for x in b}
    for i in joined:
        if i[b_name_pos] != '.':
            res[i[b_name_pos]].append(i.name)
    return res