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contracts...Whiltelist.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

/** 
 * @title Whitelist
 * @dev 
 */
contract Whitelist {

    mapping (address => bool) whitelist;    

    event Authorized(address _address);

    event SendEth(address _address, uint _value);

    function authorize(address _address) external payable {
        require(check(), "You are not allowed.");
        
        whitelist[_address] = true;

        emit Authorized(_address);
    }

    function check() private view returns(bool) {
        return whitelist[msg.sender] == true;
    }

    receive() external payable {
        emit SendEth(msg.sender, msg.value);
    }

    fallback() external payable {
        emit SendEth(msg.sender, msg.value);
    }

}