func: 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);
      }