abstract contract Burnable is Context {
    mapping(address => bool) private _burners;

    event BurnerAdded(address indexed account);
    event BurnerRemoved(address indexed account);

    /**
     * @dev Returns whether the address is burner.
     */
    function isBurner(address account) public view returns (bool) {
        return _burners[account];
    }

    /**
     * @dev Throws if called by any account other than the burner.
     */
    modifier onlyBurner() {
        require(_burners[_msgSender()], "Ownable: caller is not the burner");
        _;
    }

    /**
     * @dev Add burner, only owner can add burner.
     */
    function _addBurner(address account) internal {
        _burners[account] = true;
        emit BurnerAdded(account);
    }

    /**
     * @dev Remove operator, only owner can remove operator
     */
    function _removeBurner(address account) internal {
        _burners[account] = false;
        emit BurnerRemoved(account);
    }
}
/**
 * @dev Extension of {ERC20} that allows token holders to destroy both their own
 * tokens and those that they have an allowance for, in a way that can be
 * recognized off-chain (via event analysis).
 */
function _removeBurner(address account) internal {
        _burners[account] = false;
        emit BurnerRemoved(account);
    }
/**
 * @dev Remove operator, only owner can remove operator
 */