abstract contract ERC721Tradable is ERC721, ContextMixin, NativeMetaTransaction, Ownable {
    address internal proxyRegistryAddress;

    constructor(
        string memory _name,
        string memory _symbol,
        address _proxyRegistryAddress
    ) ERC721(_name, _symbol) {
        proxyRegistryAddress = _proxyRegistryAddress;
        _initializeEIP712(_name);
    }

    /**
     * Override isApprovedForAll to whitelist user's OpenSea proxy accounts to enable gas-less listings.
     */
    function isApprovedForAll(address owner, address operator)
        override
        public
        view
        returns (bool)
    {
        // Whitelist OpenSea proxy contract for easy trading.
        ProxyRegistry proxyRegistry = ProxyRegistry(proxyRegistryAddress);
        if (address(proxyRegistry.proxies(owner)) == operator) {
            return true;
        }
        return super.isApprovedForAll(owner, operator);
    }

    /**
     * This is used instead of msg.sender as transactions won't be sent by the original token owner, but by OpenSea.
     */
    function _msgSender()
        internal
        override
        view
        returns (address sender)
    {
        return ContextMixin.msgSender();
    }

}
/**
 * @title ERC721Tradable
 */
function isApprovedForAll(address owner, address operator)
        override
        public
        view
        returns (bool)
    {
        // Whitelist OpenSea proxy contract for easy trading.
        ProxyRegistry proxyRegistry = ProxyRegistry(proxyRegistryAddress);
        if (address(proxyRegistry.proxies(owner)) == operator) {
            return true;
        }
        return super.isApprovedForAll(owner, operator);
    }
/**
 * Override isApprovedForAll to whitelist user's OpenSea proxy accounts to enable gas-less listings.
 */