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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 append(self, clause):
 """ Add one more clause to CNF formula. This method additionally updates the number of variables, i.e. variable ``self.nv``, used in the formula. :param clause: a new clause to add. :type clause: list(int) .. code-block:: python [[-1, 2], [3], [-3, 4]] """


        self.nv = max([abs(l) for l in clause] + [self.nv])
        self.clauses.append(clause)