D.K. Nakano and J.H. Palmieri,
Support varieties for the Steenrod algebra
In this paper we study the cohomological varieties associated to the
finite-dimensional sub-Hopf algebras of the Steenrod algebra. A
stratification theorem like the Quillen/Avrunin-Scott stratification
theorem for finite groups is proven. With this stratification one can
then invoke results from restricted Lie algebra cohomology to study
these cohomological varieties. As a result, we get a description of
the cohomology of these Hopf algebras, modulo nilpotence; we also
prove a conjecture of Margolis about $P^{s}_{t}$-homology of a tensor
product of modules.