Q.E.D.

Q.E.D. is an acronym or initialism of the Latin phrase , which means "what was to be demonstrated". In other words, Q.E.D. means "something was to be proven, and now it has been done".
History.
In the European Renaissance, scholars often wrote in Latin. The phrases "Q.E.D." was often used at the end of mathematical or philosophical proofs.
Equivalents in other languages.
"Q.E.D." is used in many languages, including: