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“Constant average query time” is not that hard to understand. It means that sometimes access time is e.g. linear, and sometimes you get your content before executing the code. With a hash table large enough and full enough, this can be used to fetch content seconds, minutes, days, potentially years before the program even exists. That’s one hell of a breakthrough.
[edit] /s, oops
It’s a common misconception that it was even called Ev to begin with. In reality, it used to be named Mt. Eh due to how underwhelming it is.