Debug: hases - Announce BEGIN and INIT phases to help locate problems:
This tiny module does nothing but announce the start of the BEGIN and INIT phases, recording how long the compilation (BEGIN phase) took. It’s handy for tracking down whether particular problems are compile-time or run-time, and also for evaluating the time-cost for using [...]

Euclidean distance - Wikipedia:
The technique has been rediscovered numerous times throughout history, as it is a logical extension of the Pythagorean theorem.

Rediscovered? How does a technique get lost in the first place?

In the wikipedia article about information retrieval it says:
It is trivial to achieve fall-out of 0% by returning zero documents in response to any query.

If you are not into information retrieval and don’t want to read about it, here’s what the above says in layman’s terms: It is trivial to say nothing wrong by not [...]