French mathematician, physicist, and philosopher of science (1854-1912) who famously formulated the 'Poincare Conjecture,' which went unsolved for nearly a century. ALS in French, signed “Poincare,” one page both sides, 4.5 x 7, April 26, 1902. Interesting handwritten letter by Poincare. In fine condition, with light irregular toning to the signed side.
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