References
    ----------
    Copeland, A.H. (1951). A “reasonable” social welfare function, mimeographed. In: Seminar on applications of mathematics to the social sciences. Ann Arbor: Department of Mathematics, University of Michigan.
    &#34;&#34;&#34;

    if pw_matrix:
        m = df
        unique_alternatives = list(df)

    else:
        m, unique_alternatives = pairwise_matrix(
            df,
            alternative=alternative,
            ballot=ballot,
            delimiter=delimiter,
     