TITLE: What is the meaning of the expression Q.E.D.? Is it similar to ■ appearing at the end of a theorem?
QUESTION [15 upvotes]: I am curious about the meaning of the word Q.E.D. that is often written after a proof of a theorem (some math books use this convention). 
Edit: Is it similar to the box being placed after a proof of a theorem? Also, what is the history of the development from Q.E.D. to ■ ?

REPLY [1 votes]: The meaning of the expresson Q.E.D is express quod erat demonstrandum.
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