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In French, when concluding a demonstration, we say "CQFD", which stands for "Ce Qu'il Fallait Démontrer".

Do English has an equivalent for this ?

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I don't know French but this might be what you're looking for: en.wikipedia.org/wiki/Q.E.D. QEF would be unknown by most English Speaking people. –  dcaswell Sep 20 '13 at 15:28
    
@user814064 agreed, you should make that an answer. –  Dusty Sep 20 '13 at 15:30
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QED is what one used to put at the bottom of a mathematical prooof. Quod erat demonstrandum. That which was to be proved. I don't know if QED is anglicized enough for you or still considered full on Latin. Edit: Other people answered while I was typing. –  mikeY Sep 20 '13 at 15:31
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"This concludes the demonstration" is about it for a demonstration. Unless you're talking about mathematics, when you have proven a theorem. At the end of a proof, one may place "QED" from Quod Erat Demonstrandum 'That which was to be demonstrated'. Outside the "D" in Demonstrandum, however, Demonstration is not normally used in its mathematicological sense in English, outside a specificially logical or mathematical context. Which is not summoned up by use of the phrase "concluding a demonstration". –  John Lawler Sep 20 '13 at 15:35
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A completely language agnostic option would be to use ∎ (the tombstone mark). This is most commonly seen at the end of a proof. –  Andrew Coonce Sep 20 '13 at 20:55

1 Answer 1

up vote 12 down vote accepted

Q.E.D - Quod erat demonstrandum - is put at the end of of a proof to signify that what we attempted to prove has been proven.

Q.E.F. - Quod erat faciendum - is a term that is used in geometric proof to signify that the geometric construction has been completed. It is a rarely used English abbreviation.

From the article the correct translation is Q.E.F. but from your description Q.E.D. sounds more accurate because it comes at the end of a proof/demonstration.

Note: From the comments below CQFD is always equivalent to QED.

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So the answer is "no, there is no english acronym, use latin instead" ? –  Trajan Sep 20 '13 at 15:47
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Q.E.D. is very widely known. It would be understood by virtually everyone. Just like etc. is Latin, but everyone knows what it means. –  dcaswell Sep 20 '13 at 15:48
    
I am baffled by your assertion that the correct translation is Q.E.F. Wouldn't that be "ce qu'il fallait construire" in French? (CQFC, which doesn't seem to be used, unless I chose the wrong verb.) The wikipedia articles say both Q.E.F. and Q.E.D. are translated to CQFD in French, but the literal translation of CQFD is Q.E.D. –  Peter Shor Sep 20 '13 at 20:04
    
It's not my assertion. It's my understanding of this page: en.wikipedia.org/wiki/Q.E.D maybe falsely based on where the table occurs. As I said I don't know French. –  dcaswell Sep 20 '13 at 20:09
    
Your understanding is wrong; I know some French. –  Peter Shor Sep 20 '13 at 20:10

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