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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 _map_extlit(self, l):
 """ Map an external variable to an internal one if necessary. This method is used when new clauses are added to the formula incrementally, which may result in introducing new variables clashing with the previously used *clause selectors*. The method makes sure no clash occurs, i.e. it maps the original variables used in the new problem clauses to the newly introduced auxiliary variables (see :func:`add_clause`). Given an integer literal, a fresh literal is returned. The returned integer has the same sign as the input literal. :param l: literal to map :type l: int :rtype: int """


        v = abs(l)

        if v in self.vmap.e2i:
            return int(copysign(self.vmap.e2i[v], l))
        else:
            self.topv += 1

            self.vmap.e2i[v] = self.topv
            self.vmap.i2e[self.topv] = v

            return int(copysign(self.topv, l))