Desargues, Gérard zhārär´ dəzärg´ [key], 1591–1661, French mathematician and engineer, a founder of modern geometry. He discovered the theorems on involutions and transversals known by his name and worked on conic sections. His writings, lost for a time, were republished in 1864. His purely mathematical texts, in French, ed. by René Taton, were republished in 1951.
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