def frags_overlap_same_chrom(frags, start, end):
    """
    get the fragments overlapping the interval [start, end], assuming
    all fragments in the input table are already on the correct chromosome
    """
    f = frags.loc[((frags["start_pos"] < start) & (frags["end_pos"] > start)) |
                  ((frags["start_pos"] < end) & (frags["end_pos"] > end))]
    return f