Steenrod algebra
In algebraic topology, a Steenrod algebra was defined by Cartan (1955) to be the algebra of stable cohomology operations for mod p cohomology.
For a given prime number p, the Steenrod algebra Ap is the graded Hopf algebra over the field Fp of order p, consisting of all stable cohomology operations for mod p cohomology. It is generated by the Steenrod squares introduced by Steenrod (1947) for p=2, and by the Steenrod reduced pth powers introduced in Steenrod (1953) and the Bockstein homomorphism for p>2.