RARE compilation of essays by Élie Cartan, celebrating 50 years of his work in theoretical and applied mathematics. Cartan worked closely with Albert Einstein and expanded on his Theory of Relativity, and also explored Lie groups, differential systems, and differential geometry. 280x230 mm, 260 pages. Tan softcover. [CONDITION:] Cover worn with various small tears on edges. Outer front cover edge bent, fortified from inside with tape. Cover slightly dirty. Pages clean. [SUMMARY:] This rare collection of essays by one of the most important mathematicians of the early 20th century is visibly worn externally, but in good condition internally.