QED

See also: Q.E.D.

English

WOTD – 24 January 2020

Pronunciation

• IPA^(key): /ˌkjuːiːˈdiː/

• Audio (RP):

  (file)

• IPA^(key): /ˌkjuˌiˈdi/

Etymology 1

From Late Latin q.e.d., from Latin q(uod) e(rat) d(emonstrandum).

Phrase

(deprecated template usage) QED

1. (mathematics, dated) Initialism of quod erat demonstrandum (“what had to be proved; what was to be demonstrated”): placed at the end of a mathematical proof to show that the theorem under discussion is proved.
   • 1999, William Dunham, “Euler and Analytic Number Theory”, in Euler: The Master of Us All (The Dolciani Mathematical Expositions; 22), [Washington, D.C.]: Mathematical Association of America, →ISBN, page 64:

     By Cases 1 and 2, we see that any finite collection of $4k-1$ primes cannot contain all such primes. Thus there are infinitely many primes of this type. Q.E.D.

2. (by extension) Used to indicate that an argument or proposition is proved by the existence of some fact or scenario.

Usage notes

When used to end a mathematical proof, QED is somewhat dated or traditional; modern textbooks often use the graphical symbol ∎ (the halmos or tombstone) instead. Other languages generally use a vernacular abbreviation, such as French CQFD (“ce qu'il fallait démontrer”).

Alternative forms

• Q.E.D.

Related terms

• QEF

Translations

placed at the end of a mathematical proof to show that the theorem under discussion is proved

• Chinese:

  Mandarin: 證畢／证毕 (zhèngbì), 证毕 (zhèngbì), 證訖／证讫 (zhèngqì), 证讫 (zhèngqì)

• Czech: c.b.d. (co bylo dokázat)
• Esperanto: KEP (kio estis pruvota)
• Finnish: MOT (fi) (mikä oli todistettava)
• French: CQFD (fr) (ce qu'il fallait démontrer)
• Georgian: რ.დ.გ (r.d.g)
• German: w. z. b. w. (was zu beweisen war)
• Greek: Ό.Έ.Δ. (Ó.É.D.) (όπερ έδει δείξαι)
• Hebrew: מָשָׁ"ל (he) (masha"l), מ.ש.ל. m pl (m.sh.l.) (מה שצריך להוכיח, מה שרצינו להוכיח, etc.)
• Hindi: इ. सि. (i. si.) (इति सिद्धम्)
• (deprecated template usage) {{trans-mid}}
• Icelandic: þ.s.s.á. (það sem sanna átti)
• Italian: CVD (it) (come volevasi dimostrare)
• Japanese: 証明終わり (しょうめいおわり, shōmei owari)
• Polish: c.b.d.o. (pl), c.b.d.u.
• Portuguese: CQD, QED
• Russian: ч. т. д. (ru) (č. t. d.), что и тре́бовалось доказа́ть (ru) (što i trébovalosʹ dokazátʹ)
• Slovak: Č.B.T.D. (čo bolo treba dokázať)
• Spanish: C.Q.D., como queríamos demostrar
• Swedish: VSV (sv) (vilket skulle visas), VSB (sv) (vilket skulle bevisas)
• Vietnamese: đpcm (vi)

Noun

QED (plural QEDs)

1. Some fact or scenario that proves an argument or proposition; a justification.

Alternative forms

• Q.E.D.

Translations

fact or scenario that proves an argument or proposition — see justification

Etymology 2

From q(uantum) e(lectro)d(ynamics).

Noun

QED (uncountable)

1. (physics) (Partial) initialism of quantum electrodynamics.
   • 2011, Brian Cox, Jeff Forshaw, “Interaction”, in The Quantum Universe: Everything that Can Happen Does Happen, London: Allen Lane, →ISBN, page 176:

     QED is the theory that explains how electrically charged particles, like electrons, interact with each other and with particles of light (photons). [...] Pretty much everything else – certainly everything you see and feel around you – is explained at the deepest known level by QED. Matter, light, electricity and magnetism – it is all QED.

Related terms

• QCD (“(partial) initialism of quantum chromodynamics”)

Further reading

• Q.E.D. on Wikipedia.Wikipedia
• quantum electrodynamics on Wikipedia.Wikipedia

Anagrams

• DEQ

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Latin

Phrase

QED

1. QED (“quod erat demonstrandum”) Initialism of quod erat demonstrandum.

Descendants

• English: QED (“quod erat demonstrandum”)

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Portuguese

Etymology

Borrowed from Latin QED.

Phrase

1. (sciences) QED

Synonyms

• CQD