\begin{definition}[Definition:QEI]
The initials of '''Quod Erat Inveniendum''', which is {{WP|Latin|Latin}} for '''which was to be found'''.
These initials were traditionally added after the completion of a calculation (either arithmetic or algebraic).
This is practically never seen nowadays outside translations of historical texts.
If there were ever a need for such an indication, the Halmos symbol $\blacksquare$ would be used instead.
{{ProofWiki}} does not bother to distinguish between use of '''QEI''' and the better-known '''QED''', and recommends the use of the {{TL|qed}} template exclusively instead.
\end{definition}