Leray in Oflag XVIIA: The origins of sheaf theory, sheaf cohomology, and spectral sequences

Jean Leray (November 7, 1906–November 10, 1998) was confined to an officers’ prison camp (“Oflag”) in Austria for the whole of World War II. There he took up algebraic topology, and the result was a spectacular flowering of highly original ideas, ideas which have, through the usual metamorphism of history, shaped the course of mathematics in the sixty years since then. Today we would divide his discoveries into three parts: sheaves, sheaf cohomology, and spectral sequences. For the most part these ideas became known only after the war ended, and fully five more years passed before they became widely understood. They now stand at the very heart of much of modern mathematics. I will try to describe them, how Leray may have come to them, and the reception they received.