Carl Gustav Axel Harnack

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Carl Gustav Axel Harnack (7 May [O.S. 25 April] 1851, Dorpat (now Tartu) – 3 April 1888, Dresden) was a Baltic German mathematician who contributed to potential theory. Harnack's inequality applied to harmonic functions. He also worked on the real algebraic geometry of plane curves, proving Harnack's curve theorem for real plane algebraic curves.