Q.E.D. (quod erat demonstrandum)

The traditional 'mic-drop' at the end of a mathematical proof — 'this is what we set out to prove, and now we've proved it.'

Origin

The Latin phrase translates Euclid's Greek hoper edei deixai. Mathematicians have been ending proofs with Q.E.D. (or the printed tombstone symbol ∎) for centuries. The Renaissance editions of Euclid's Elements made the abbreviation universal.

Modern usage

Used in mathematics writing, philosophy, and (heavily) in any internet argument where the speaker thinks they've just won. 'Q.E.D.' at the end of a tweet is almost always smug and almost always premature.

In the wild

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