Definition:Equals/Historical Note

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Historical Note on Equals

The equals sign was introduced by Robert Recorde in his $1557$ work The Whetstone of Witte.

Placing two long hyphens together, one above the other, he wrote:

To avoide the tediouse repetition of these woordes: is equalle to: I will sette as I doe often in woorke use, a paire of paralleles, or gemowe lines of one lengthe: $= \!\!\! = \!\!\! = \!\!\! = \!\!\! = \!\!\! = \!\!\! =$, bicause noe .2. thynges, can be moare equalle.

The word gemowe comes from the Latin geminus meaning twin.

François Viète used the symbol $\sim$, while René Descartes used $\propto$.

Both were in due course supplanted by $=$, a shortened and hence more efficient version of Recorde's invention.

It is suggested by some sources that this was mainly through the influence of Leibniz.