Latin for "which was to be found," quod erat inveniendum is sometimes stated at the end of a mathematic calculation which has just been completed, usually abbreviated QEI. Like QED and QEF, it largely performs as a stylistic indication that the mathematical operation has been completed as its author intended, and there is nothing further to be added to it; it also implies that nothing else should need to be added, in order to read and understand the calculation as an outside party. Unlike QED and QEF, it would not be used for proofs, theorems, or geometric constructions.
QEI is itself a translation into Latin from Greek ὅπερ ἔδει εὐρεῖν, of the same meaning, as used by Euclid, Archimedes, and other Greek mathematicicans and philosophers of Ancient Greece.
Iron Noder 2016, 3/30