erat
Latin phrase(quod erat de-mon-stran-dum)
which (is what) was to be shown (originally) —abbreviation QED—used at the end of a logical or mathematical proof
erat
Latin phrase(quod erat de-mon-stran-dum)
which (is what) was to be done (originally) —abbreviation q.e.f.—used at the end of a geometrical construction