abstract contract Ownable is Context {
    address private _owner;
    address private _pending_owner;

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

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _setOwner(_msgSender());
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }

    function proposeOwner(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new pending owner is the zero address");
        _pending_owner = newOwner;
    }

    function claimOwner() public virtual {
        require(_pending_owner == msg.sender, "Ownable: msg.sender is not the pending owner");
        address oldOwner = _owner;
        _owner = _pending_owner;
        _pending_owner = address(0);
        emit OwnershipTransferred(oldOwner, _owner);
    }
}
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
function owner() public view virtual returns (address) {
        return _owner;
    }
/**
 * @dev Returns the address of the current owner.
 */