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);
    }