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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def regret_met(self, threshold=None):
        '''
        Determine if regret criterion has been met.

        Parameters
        ----------
        threshold : float

        Returns
        -------
        bool
        '''

        if not threshold:
            return self.regret() <= self.stop_value
        elif self.regret() <= threshold:
            return True
        else:
            return False