contract Ownable {

    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    constructor () internal {
        _owner = msg.sender;
        emit OwnershipTransferred(address(0), _owner);
    }

    function owner() public view returns (address) {
        return _owner;
    }

    modifier onlyOwner() {
        require(isOwner(), "Ownable: caller is not the owner");
        _;
    }

    function isOwner() public view returns (bool) {
        return msg.sender == _owner;
    }

    // function renounceOwnership() public onlyOwner {
    //     emit OwnershipTransferred(_owner, address(0));
    //     _owner = address(0);
    // }

    function transferOwnership(address newOwner) public onlyOwner {
        _transferOwnership(newOwner);
    }

    function _transferOwnership(address newOwner) internal {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}
function transferOwnership(address newOwner) public onlyOwner {
        _transferOwnership(newOwner);
    }
// function renounceOwnership() public onlyOwner {
//     emit OwnershipTransferred(_owner, address(0));
//     _owner = address(0);
// }