Latin. quod erat demonstrandum (which was to be demonstrated). the abbreviation of the Latin phrase quod erat demonstrandum , used to say that a fact or event proves that what you say is true
a relativistic quantum theory of the electromagnetic interactions of photons and electrons and muons
A latin abbreviation for quod erat demonstrandum It means "which was to be shown" in english It is used at the end of a proof to show that the proof has been completed