def sim(self, src, tar):
return mra_compare(src, tar) / <NUM_LIT:6><EOL>
Return the normalized MRA similarity of two strings.

        This is the MRA normalized to :math:`[0, 1]`, given that MRA itself is
        constrained to the range :math:`[0, 6]`.

        Parameters
        ----------
        src : str
            Source string for comparison
        tar : str
            Target string for comparison

        Returns
        -------
        float
            Normalized MRA similarity

        Examples
        --------
        >>> cmp = MRA()
        >>> cmp.sim('cat', 'hat')
        0.8333333333333334
        >>> cmp.sim('Niall', 'Neil')
        1.0
        >>> cmp.sim('aluminum', 'Catalan')
        0.0
        >>> cmp.sim('ATCG', 'TAGC')
        0.8333333333333334