contract LibOwnable {
    address private _owner;

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

    /// @dev The Ownable constructor sets the original `owner` of the contract to the sender account.
    constructor() internal {
        _owner = msg.sender;
        emit OwnershipTransferred(address(0), _owner);
    }

    /// @return the address of the owner.
    function owner() public view returns(address) {
        return _owner;
    }

    /// @dev Throws if called by any account other than the owner.
    modifier onlyOwner() {
        require(isOwner(), "NOT_OWNER");
        _;
    }

    /// @return true if `msg.sender` is the owner of the contract.
    function isOwner() public view returns(bool) {
        return msg.sender == _owner;
    }

    /// @dev Allows the current owner to relinquish control of the contract.
    /// @notice Renouncing to ownership will leave the contract without an owner.
    /// It will not be possible to call the functions with the `onlyOwner`
    /// modifier anymore.
    function renounceOwnership() public onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /// @dev Allows the current owner to transfer control of the contract to a newOwner.
    /// @param newOwner The address to transfer ownership to.
    function transferOwnership(address newOwner) public onlyOwner {
        require(newOwner != address(0), "INVALID_OWNER");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}
/// @title Ownable
/// @dev The Ownable contract has an owner address, and provides basic authorization control
/// functions, this simplifies the implementation of "user permissions".
function isOwner() public view returns(bool) {
    return msg.sender == _owner;
}

/// @return true if `msg.sender` is the owner of the contract.