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Meanwhile, in the academic scene, researchers found many applications for proof of work besides spam, such as preventing denial-of-service at-tacks,25 ensuring the integrity of Web analytics,17 and rate-limiting password guessing online.38 Incidentally, the term proof of work was coined only in 1999 in a paper by Markus Jakobsson and Ari Juels, which also includes a nice survey of the work up until that point.24 It is worth noting that these researchers seem to have been unaware of hashcash but...