def merge(self, other, successor=None):
        """
        Merge two abstract states.

        :param VariableRecoveryState other: The other abstract state to merge.
        :return:                            The merged abstract state.
        :rtype:                             VariableRecoveryState
        """

        replacements = {}
        if successor in self.dominance_frontiers:
            replacements = self._make_phi_variables(successor, self, other)

        merged_concrete_states =  [ self._concrete_states[0] ] # self._merge_concrete_states(other)

        new_stack_region = self.stack_region.copy().replace(replacements)
        new_stack_region.merge(other.stack_region, replacements=replacements)

        new_register_region = self.register_region.copy().replace(replacements)
        new_register_region.merge(other.register_region, replacements=replacements)

        return VariableRecoveryState(successor, self._analysis, self.arch, self.function, merged_concrete_states,
                                     stack_region=new_stack_region,
                                     register_region=new_register_region
                                     )