solve dict of rpn expressions to pure var to val dict
        :param rpndict: dict of rpn expressions
        return pure var to val dict

def resolve_rpn(self, rpndict):
        """ solve dict of rpn expressions to pure var to val dict
        :param rpndict: dict of rpn expressions
        return pure var to val dict
        """
        if rpndict == {}:
            return {}

        retflag = self.get_rpndict_flag(rpndict)
        cnt = 0
        tmpdict = {k: v for k, v in rpndict.items()}
        while not retflag:
            # update rpndict
            cnt += 1
            tmpdict = self.update_rpndict(tmpdict)
            # and flag
            retflag = self.get_rpndict_flag(tmpdict)
        return tmpdict