def append_formula(self, formula, no_return=True):
        """
            This method can be used to add a given list of clauses into the
            solver.

            :param formula: a list of clauses.
            :param no_return: check solver's internal formula and return the
                result, if set to ``False``.

            :type formula: iterable(iterable(int))
            :type no_return: bool

            The ``no_return`` argument is set to ``True`` by default.

            :rtype: bool if ``no_return`` is set to ``False``.

            .. code-block:: python

                >>> cnf = CNF()
                ... # assume the formula contains clauses
                >>> s = Solver()
                >>> s.append_formula(cnf.clauses, no_return=False)
                True
        """

        if self.solver:
            res = self.solver.append_formula(formula, no_return)
            if not no_return:
                return res