A special mathematical term that means "because".

Swiss mathematician John Rehn first used ∴. In the math book Teusche Algebra published in 1659, he used two symbols "∴" and "⊙" to express "so", among which "∴" was used more.

Extended data:

1805 The word "because" was first used in The Gentleman's Mathematical Companion published in Britain, but it did not catch on.

By 1827, Euclid's Elements of Geometry published by Cambridge University used ⊙ for "because" and ∴ for "so" respectively. This usage has become more and more popular and has been used ever since.

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