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# System prepended metadata

title: Blockchain course 3/16

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# Blockchain course 3/16

## PoW property 1/3 diffcult of computing

PoW(proof of work)

* in 2020, about \\( 10^{21} \\) hash/block

## PoW property 2/3

* node re-caculate the target (256 byte) 2016 every block


## PoW property 3/3
* Nonce must be publiced 
* H(nonce )

## Mining economic

## Rule of game



