contract Ownable {
    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() public {
        _owner = msg.sender;
    }

    /**
    * @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() internal view returns(bool) {
        return msg.sender == _owner;
    }

    /**
    * @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 {
        _transferOwnership(newOwner);
    }

    /**
    * @dev Transfers control of the contract to a newOwner.
    * @param newOwner The address to transfer ownership to.
    */
    function _transferOwnership(address newOwner) internal {
        require(newOwner != address(0));
        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() internal view returns(bool) {
        return msg.sender == _owner;
    }
/**
 * @return true if `msg.sender` is the owner of the contract.
 */