contract Ownable is Context {
    address private _owner;

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

    /**
     * @dev The Ownable constructor sets the original `owner` of the contract to the sender
     * account.
     */
    constructor () public {
        _owner = _msgSender();
        emit OwnerChanged(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());
        _;
    }

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


    /**
     * @dev Allows the current owner to transfer control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function changeOwnership(address newOwner) public onlyOwner {
        _changeOwnership(newOwner);
    }

    /**
     * @dev Transfers control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function _changeOwnership(address newOwner) internal {
        require(newOwner != address(0));
        require(newOwner != _owner);
        emit OwnerChanged(_owner, newOwner);
        _owner = newOwner;
    }
}
function isOwner() public view returns (bool) {
    return _msgSender() == _owner;
}

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