StarkNet and Cairo let you use inputs like "Use the value of variable X in contract Y at block Z of Ethereum/Bitcoin/whatever, and do something with it". In a trustless manner.

Remember earlier, when we talked about how it was hard for chains to understand each other? Let's say you want chain A to read chain B's state. Not "receive a message from B". "Read inside of B".

This would cost a lot of gas. Chain A would have to check the correct execution of B; receive its state at a given height; and read from it. Very expensive... unless …wait for it…..computation is cheap.

In that case, you can a) generate a proof of execution for chain B up to a certain height b) provide the state at this point c) go through it to find the value(s) you're looking for No storing involved, just computing. Cheap.

Okay, so what can you do with that? You can extract trustlessly a snapshot of token balances at a given height, for trustless token-weighted voting. Ping @SnapshotLabs

For people who like both BTC and ETH: Do atomic swaps and prove you own bitcoins utxos. You can show what the content of an op_return hash actually was You can extend a multisig from Bitcoin to Ethereum

It's easy to prove that you used @CurveFinance before it was cool (ping @DegenScore ) Or play with an NFT on chain B (ping @TheDopeWars ) and prove you own it on chain A You could check out the repo and start building stuff, anon!.

By using SPs, you can copy/pasta data trustlessly from any contract, from any chain, at any time. They are like CRISPR/Cas9, for blockchain devs.

Next up: f r a c t a l s c a l i n g