function approve(address spender, uint256 value) public returns (bool);
    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 value
    );
}


contract BulDex is Ownable {
    using SafeERC20 for ERC20;

    mapping(address => bool) users;

    ERC20 public promoToken;
    ERC20 public bullToken;

    uint public minVal = 365000000000000000000;
    uint public bullAmount = 3140000000000000000;

    constructor(address _promoToken, address _bullToken) public {
        promoToken = ERC20(_promoToken);
        bullToken = ERC20(_bullToken);
    }