 Eric is asking about the Byzantine general's dilemma with physical coins and paper wallets. Suppose three persons have no access to the internet when they seek to exchange value in cryptocurrency. They have only their paper wallets and physical crypto coins. How do they overcome the Byzantine general's dilemma? Afterwards, they get on the internet and could update the blockchain with the exchange that took place offline. How does that work? How does that affect the Byzantine general's dilemma? Eric, if you do not have access to the blockchain, then you cannot, in fact, resolve the Byzantine general's dilemma. Specifically, the subset of Byzantine fault tolerance, which is the double-spend problem. I am holding crypto coins in a physical device, let's say a paper wallet, or some kind of other device, like a stick. OpenDime would be a good example, a crypto token, which contains a private key in it. I am trying to do a transaction with someone. How does the other person know that the coins on that stick are still available? This is a difficult problem to solve, because even if I have a full copy of the blockchain, let's say I synced it all to my laptop before I went on a trip, and I have the information up to last week. I can actually take the Bitcoin address, or some of the public identifier, from a paper wallet or a cryptosdick. I can verify that at some point in the past there was Bitcoin on there. But I don't know if that Bitcoin has been spent. A whole week has passed. I am out of date. I no longer have an up-to-date copy of the blockchain, and I don't have any idea of the current mempool. So I have no copy of the mempool, no copy of the blockchain. I can't solve the Byzantine general's dilemma. I could take a risk. But at that point, I can't use those technologies to assure myself. There are some interesting options there. If somebody presented me with an up-to-date copy of the blockchain with proof of work in it, I could then validate up to the last block issued, and have a much, much higher degree of certainty that the coins have not been spent. Again, not 100%, because I don't know if there is a transaction currently being propagated, about to go into the next block that spends these coins from right underneath my feet. But I do know a bit more if I have a latest copy. One of the interesting solutions to this problem is the understanding that participating in the Bitcoin blockchain is a highly asymmetric function. You need to download gigabytes of data in order to receive the blockchain, and receive the stream of real-time transactions. But you only need to update 350 bytes. You only need to upload 350 bytes or so to make a transaction. One of the best ways of doing that is with a satellite feed, because you can scale that very nicely. You can have an infinite number of receiving stations, receiving from a single broadcast satellite, receiving blocks and transactions, and you can then transmit your own transaction, which is 350 bytes, using a text message to a gateway that injects it onto the Bitcoin network, or a very low bandwidth transmission system. The first satellite transmission mechanism was introduced recently. You can envision a situation where you even have a field-capable kit, where you just pop up a foldable satellite dish, a solar panel, and a software-defined radio for your laptop, and you can sync the blockchain anywhere in the world, where the satellite coverage exists, of course.