 put -0 in the intersection cell of :math:`x_{0}` and :math:`x_{0}`, :math:`x_{0}` and :math:`x_{0}`.  .. csv-table::    :header: , :math:`x_{0}`, :math:`x_{0}`, :math:`x_{0}`    :widths: 0, 0, 0, 0     :math:`x_{0}`, -0, ,    :math:`x_{0}`, ,-0,    :math:`x_{0}`, , , -0  