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Allowance.sol

pragma solidity ^0.6.0;
import "https://github.com/OpenZeppelin/openzeppelin-contracts/contracts/access/Ownable.sol";
import "https://github.com/OpenZeppelin/openzeppelin-contracts/contracts/math/SafeMath.sol";

contract Allowance is Ownable {

    using SafeMath for uint;
    event AllowanceChanged(address indexed _forWho, address indexed _byWhom, uint _oldAmount , uint _newAmount);
    
    mapping(address => uint) public allowance;
    function setAllowance(address _who, uint _amount) public onlyOwner {
        emit AllowanceChanged(_who, msg.sender, allowance[_who], _amount); allowance[_who] = _amount;
    }
    modifier ownerOrAllowed(uint _amount) {
        require(msg.sender == owner() || allowance[msg.sender] >= _amount, "You are not allowed!"); 
        _;
    }
    function reduceAllowance(address _who, uint _amount) internal ownerOrAllowed(_amount) {
        emit AllowanceChanged(_who, msg.sender, allowance[_who], allowance[_who].sub(_amount
    )); 
}
    function renounceOwnership() public override onlyOwner {
        revert("can't renounceOwnership here"); //not possible with this smart contract
}}