We give a conceptual clarification of Milnor's theorem, which tells us the Hopf algebra structure of the stable co-operations in the odd primary ordinary cohomology. Directly connecting with the quasi-strict automorphism group of some -dimensional additive formal group law and modular invariants, we give a new proof of this theorem of Milnor.
Masateru INOUE. "Odd primary Steenrod algebra, additive formal group laws, and modular invariants." J. Math. Soc. Japan 58 (2) 311 - 332, April, 2006. https://doi.org/10.2969/jmsj/1149166777