def get_corefs(df, matches):
    """
    Add corefs to a set of matches
    """
    out = set()
    df = df['c']
    for s, i in matches:
        out.add((s, i))
        coline = df[s, i]
        if coline.endswith('*'):
            same_co = df[df == coline]
            for ix in same_co.index:
                out.add(ix)
    return out
