Q.E.D.
- For other meanings of the abbreviation "QED", see QED.
Q. E. D. is an abbreviation of the Latin phrase "quod erat demonstrandum" (literally, "that which was to be demonstrated"). Q.E.D. may be written at the end of mathematical proofs to show that the result required for the proof to be complete has been obtained. It is not seen as frequently now as in earlier centuries.
End-of-proof symbolism in the present day is often the symbol ■ (solid black square) called the tombstone or halmos (after Paul Halmos who pioneered its use). The tombstone is sometimes open; □ (hollow black square). Another simple way of stating that the proof is complete is to simply write "proven" or "shown" in parenthesis after the final step of the proof.
In Hong Kong, students jokingly reinterpret Q.E.D. as "Question Easy Done" (in Chinglish) after they finish a "difficult" mathematical proof in their schoolwork. Similarly, in English speaking countries the letters can also mean "Quite Easily Done" or, occasionally, "Quite Eloquently Done".
