def keep_form_with_max_profit(self, forms=None):
        """
        This converts the dataframe, which shows all profitable forms,
        to the form with the greatest profit, so that more profitable
        forms outcompete less profitable forms.

        Parameters
        ----------
        forms: list of strings
            List of forms which compete which other.  Can leave some out.

        Returns
        -------
        Nothing.  Goes from a multi-index to a single index with only the
        most profitable form.
        """
        f = self.feasibility

        if forms is not None:
            f = f[forms]

        if len(f) > 0:
            mu = self._max_form(f, "max_profit")
            indexes = [tuple(x) for x in mu.reset_index().values]
        else:
            indexes = []
        df = f.stack(level=0).loc[indexes]
        df.index.names = ["parcel_id", "form"]
        df = df.reset_index(level=1)
        return df