docs: 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
                                       )