These are things named after Ernst Witt, a German mathematician. Bourbaki–Witt theorem Hall–Witt identity Hasse–Witt matrix Hasse–Witt invariant Poincaré–Birkhoff–Witt theorem, usually known as the PBW theorem Shirshov–Witt theorem Witt algebra Witt decomposition Witt design (Witt geometry) Witt group Witt index Witt polynomial Witt ring Grothendieck-Witt ring Witt scheme Witt's theorem Witt vector Witt vector cohomology