"Q.E.F.," sometimes written "QEF," is an abbreviation for the Latin phrase "quod erat faciendum" ("that which was to be done"). It is a translation of the Greek words used by Euclid to indicate the end of the justification of a construction, while "Q.E.D." was the corresponding end of proof of a theorem (cf. Heath 1956, pp. 124-129).
Q.E.F.
See also
Proof, Q.E.D.Portions of this entry contributed by Mario D'Angelo
Portions of this entry contributed by Luis Miguel Felix
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References
Heath, T. L. The Thirteen Books of the Elements, 2nd ed., Vol. 1: Books I and II. New York: Dover, 1956.Newton, I. The Principia. 1686. Reprinted by Berkeley, CA: University of California Press, p. 124, 1999.Referenced on Wolfram|Alpha
Q.E.F.Cite this as:
D'Angelo, Mario; Felix, Luis Miguel; and Weisstein, Eric W. "Q.E.F.." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/QEF.html