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In math, proofs are often accompanied by 'QED' (quod erat demonstrandum) at the end, indicating their conclusion. Some authors use a square symbol ($\square$) instead of QED, with the same meaning. Can we say $\square$ is an alias for QED? If not, what would be the best word?

sam wolfe
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    It is regularly used and in fact has this meaning. – Peter Oct 26 '22 at 14:56
  • I don't know if this is what you are looking for, but here is some info on the symbol. https://en.wikipedia.org/wiki/Tombstone_(typography) – Hagamena Oct 26 '22 at 14:59
  • The typographical term for the symbol is tombstone. If wikipedia is to be held reputable in this regard, it was already in use in some magazines as a symbol that indicated the end of an article, and for the similar purpose of indicating the end of a proof it was introduced by Halmos. So more than being synonymous with Q.E.D., it rather supplanted it by serving its traditional purpose. That is, I would not expect people anywhere to understand $\square$ as quod erat demonstrandum, certainly not out of context. – Sassatelli Giulio Oct 26 '22 at 15:03
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    Wikipedia says that the graphical form varies, but I was once told, that if do you it, you should leave it empty, then the reader can fill it in when they have understood the proof. – Henrik supports the community Oct 26 '22 at 15:21

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It is not accurate to say that symbol $\square$ has the same meaning as QED. It is simply a marker for the end of a proof, while QED is an actual statement that the proof is complete. But they do appear in the same place...

PierreCarre
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