function transfer(address _to, uint256 _tokenId) 
        senderVerify()
        public
    {
        require (msg.sender == cardList[_tokenId].playerAddress, "The card does not belong to you");
        require(_to != address(0), "Address error");
        require(_to == cardIndexToApproved[_tokenId], "Without permission");
        
        cardList[_tokenId].playerAddress = _to;
        
        if(cardIndexToApproved[_tokenId] != address(0))
            delete cardIndexToApproved[_tokenId];
        
        emit Transfer(msg.sender, _to, _tokenId);
    }