Odd primary Steenrod algebra, additive formal group laws, and modular invariants

Abstract

We give a conceptual clarification of Milnor's theorem, which tells us the Hopf algebra structure of the stable co-operations $H_{*}H$ in the odd primary ordinary cohomology. Directly connecting $H_{*}H$ with the quasi-strict automorphism group of some $1$-dimensional additive formal group law and modular invariants, we give a new proof of this theorem of Milnor.