def consensus(self, vs=None):
        r"""Return the consensus of a function over a sequence of N variables.

        The *vs* argument is a sequence of :math:`N` Boolean variables.

        The *consensus* of :math:`f(x_1, x_2, \dots, x_i, \dots, x_n)` with
        respect to variable :math:`x_i` is:
        :math:`C_{x_i}(f) = f_{x_i} \cdot f_{x_i'}`

        This is the same as the universal quantification operator:
        :math:`\forall \{x_1, x_2, \dots\} \: f`
        """
        return functools.reduce(operator.and_, self.iter_cofactors(vs))