The function claim is used by users to claim their ERC721 receipts for rewards. By using the function the receipt is set as claimed with a simple mapping id => bool, but it isnt burned. In the protocol docs it is clearly stated that users are free to sell or trade their receipts. Since the claimed receipts arent burned, this bring the risk where already claimed receipts can be sold to other people. A burn function already exists in RabbitHoleReceipt, but isnt used.
