Q.E.D, H.E.Q.D.I, H.E.Q.D.P, Q.D.I, Q.F.I, and all that

Today’s “Word of the day” from the Oxford English Dictionary is quod erat demonstrandum (which prompts the question of the largest number of words in an OED “word”, but let us leave that aside for now).

The full entry shows latin translators of Euclid toiling mightily to catch just the right sizzle of the Greek “ὅπερ ἔδει δεῖξαι” (which, we are told, means literally “what needed to be [shown] has been shown”), just like Joyce or Wodehouse trying to find the perfect mot juste for their latest novel.

So were tried, in turn, hoc est quad demonstrare intendimus (“This is what we intended to demonstrate”, too pedestrian); hoc est quod demonstrare proposimum (“This is what we proposed to demonstrate”, too egocentric); quod demonstrare intendimus (“What we intended to demonstrate”; dashing, but reeks of false modesty); quod fuit propositum (“Which was proposed”, yes, it was proposed, but is it proved?) — and who knows how many other versions which go unmentioned.

I personally think that the Greek sounds and reads much better; this suggests introducing the abbreviation “ὅἔδ”, or the transliteration “OED” if needed, instead of “QED” in the more refined mathematical literature…

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I am a professor of mathematics at ETH Zürich since 2008.

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