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While researching the term Q.E.D last night, the phrase Q.E.F was mentioned, which was apparently "used by Euclid to indicate the end of the justification of a construction".

Does Q.E.F indicate the construction can be totally described given the information given above?

Or is it simply something like the period at the end of a sentence: "this is all I'm going to say about the construction at this time"?

http://aleph0.clarku.edu/~djoyce/java/elements/bookI/propI1.html

Jemmy
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Allyl Isocyanate
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  • Quod erat faciendum "What was to make/be done". – Daniel Fischer Oct 07 '14 at 15:02
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    It's just a phrase, so it should be used where appropriate. One "makes" or "does" a construction, and "proves" or "demonstrates" a theorem. So, QEF when a construction is finished, and QED when a proof is finished. – MPW Oct 07 '14 at 15:04
  • The linked article seems to give a pretty good description... "The Q.E.F. at the end of the proof is an abbreviation for the Latin words quod erat faciendum which means “which was to be done.” A few of the propositions, as this one and the next two, solve problems by constructions. These are the ones that end with Q.E.F." – Jemmy Oct 07 '14 at 15:04
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    I doubt greatly Euclides used a latin phrase to end his proofs.... – Timbuc Oct 07 '14 at 15:21
  • When Euclid lived, the Romans were still a fairly minor Italian tribe. – André Nicolas Oct 07 '14 at 16:40

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