contract WhiteList is Ownable {

    mapping(address => uint256) public whiter;

    event AppendWhiter(address adder);
    event RemoveWhiter(address remover);

    /**
     * @notice Only onwer can append address into whitelist
     * @param account The address not added, can added to the whitelist
     */
    function appendWhiter(address account) public onlyOwner {
        require(account != address(0), "WhiteList: address not zero");
        require(
            isNotWhiter(account),
            "WhiteListe: the account exsit whilteList yet"
        );
        whiter[account] = 1;
        emit AppendWhiter(account);
    }

    /**
     * @notice Only onwer can remove address into whitelist
     * @param account The address in whitelist yet
     */
    function removeWhiter(address account) public onlyOwner {
        require(
            isWhiter(account),
            "WhiteListe: the account not exist whilteList"
        );
        delete whiter[account];
        emit RemoveWhiter(account);
    }

    /**
     * @notice Check whether acccount in whitelist
     * @param account Any address
     */
    function isWhiter(address account) public view returns (bool) {
        return whiter[account] == 1;
    }

    /**
     * @notice Check whether acccount not in whitelist
     * @param account Any address
     */
    function isNotWhiter(address account) public view returns (bool) {
        return whiter[account] != 1;
    }

}
function isNotWhiter(address account) public view returns (bool) {
    return whiter[account] != 1;
}

/**
 * @notice Check whether acccount not in whitelist
 * @param account Any address
 */