To unknowingly invent something which already exists.

Named after mathematician Gottfried Wilhelm Leibniz, who thought his fancy maths were something new, but in reality they had already been found 8 years earlier by Isaac Newton.
You know that dissertation I was working on lately? Well, turns out I pulled a Leibniz: the whole thing was already discovered centuries ago by some German scientist.
by Fenhl December 24, 2013
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