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this question confused me long time. What will other nodes exactly do in relaying transaction process? I read some questions/answers, I know they will follow ethereum protocol, but what would this protocols do? for example it invoke a contract function in a transaction and change the contract state, does other nodes need run the contract and compare with anything got from the transaction ? In bitcoin, I know other nodes will check the transaction inputs and output and so on. And If they got new block, they also will do similiar sanity check. But I don't know in ethereum, bcz it adds contract. Or please could anyone point me where I can find answers in the source code. Thank you.