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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 _popup(self):
 """recursively find commutative binary operator among child formulas and pop up them at the same level"""

        res = ()
        for child in self.formulas:
            if type(child) == type(self):
                superchilds = child.formulas
                res += superchilds
            else:
                res += (child, )
        return tuple(res)