In topology, a branch of mathematics, Borel's theorem, due to Armand Borel (1953), says the cohomology ring of a classifying space or a classifying stack is a polynomial ring.
See also Atiyah–Bott formula
Notes
References Borel, Armand (1953). "Sur la cohomologie des éspaces fibrés principaux et des éspaces homogènes de groupes de Lie compacts". Annals of Mathematics. 57 (1): 115–207. doi:10.2307/1969728. JSTOR 1969728. MR 0051508. Behrend, Kai A. (2003). "Derived l-adic categories for algebraic stacks". Memoirs of the American Mathematical Society. 163 (774). doi:10.1090/memo/0774. MR 1963494.