function LandSale(address _wallet, uint256 _goal,
                        uint256 _openingTime, uint256 _closingTime) public {
        require(_wallet != address(0));
        require(_goal > 0);
        require(_openingTime >= block.timestamp);
        require(_closingTime >= _openingTime);

        wallet = _wallet;
        vault = new RefundVault(wallet);
        goal = _goal;
        openingTime = _openingTime;
        closingTime = _closingTime;
    }