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   An up-and-coming slaver writes a blockchains.  "SlaverCoin".  It's a
   fork of bitcoin, since bitcoin is the most well-known.
   SlaverCoin
   Consensus rule:  If you use nonhuman labor to mine sha256d, we get to
   enslave you.  Slaves must be given in proportion to traded coin, freely
   divisible.
   SlaverCoin is a big hit.  Gets all the advertisements.  Everybody
   thinks it's a joke until people move in as servants when they buy
   coins.
   Physical addressea are directly asssociated with crytographic
   addresses, so that the purchased and sold slaves know where to go.
   A slavercoin kid discovers that non-slavercoin slaves are sharing their
   stories on other blockchains, and wants to try it out.
   Meanwhile, on other blockchains, wealthy investors are getting a rise
   out of freeing slaves.
   ...