Banach, Stefan stĕ´fän bä´näkh [key], 1892–1945, Polish mathematician. He was educated at the Institute of Technology in Lviv; his doctoral thesis laid the foundations of modern functional analysis, which he continued to work at throughout his life. He also made fundamental contributions to general topology, set theory, the theory of measure and integration, and the general theory of linear spaces, or vector spaces, e.g., Théorie des opérations linéaires (1932). He introduced and developed the concept of complete normed linear spaces, now called Banach spaces.
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