func: function change_city(address _sender, uint16 go_city) private{
          require(!all_stop);
          require(owner_slave_amount >= 1);
          require(!player_info[_sender].unmovable,"不可移動"); 
          
          uint16 random = uint16((keccak256(abi.encodePacked(now, random_seed))));
          random_seed.add(1);
          
          uint16 tot_domains = inquire_city_totdomains(go_city);
          uint16 go_domains_id = random % tot_domains; 
          
          player_info[_sender].city = go_city;
          player_info[_sender].domain = go_domains_id;
          
          
          address city_address = owner_slave[go_city];
          address domain_owner = ERC721_interface(city_address).ownerOf(go_domains_id);
          
          if (domain_owner != 0x0){
              if(domain_owner == _sender){
                  player_info[_sender].build = true; 
                  
              }
              else{
                  player_info[_sender].unmovable = true; 
                  player_info[msg.sender].reward = false;
              }
  		}
           
          emit Change_city(_sender, go_city, go_domains_id, player_info[_sender].unmovable);
      }