function receiverWithdraw()
        public
    {
        require(msg.sender == receiver);
        require(totalAmountRaised >= minimumAmountRequired);
        require(this.balance > 0);
        require(block.timestamp < (timeStarted + expirationInSeconds));
        require(hasBeenClaimed == false);

        hasBeenClaimed = true;
        receiver.transfer(this.balance);
        
        
    }