French mathematician, physicist, and philosopher of science (1854-1912) who famously formulated the 'Poincare Conjecture,' which went unsolved for nearly a century. AQS in French signed "Poincare," penned on an off-white 4 x 5.5 autograph card, which reads, in full: "Mais qu'est-ce que la vérité?" or 'But what is the truth?' Caption to lower border indicates that the signature derives from the collection of Alfred Brust. In fine condition.