Nested Frobenius extensions of graded superrings

Abstract

We prove a nesting phenomenon for twisted Frobenius extensions. Namely, suppose $R\subseteq B\subseteq A$ are graded superrings such that $A$ and $B$ are both twisted Frobenius extensions of $R$, $R$ is contained in the center of $A$, and $A$ is projective over $B$. Our main result is that, under these assumptions, $A$ is a twisted Frobenius extension of $B$. This generalizes a result of Pike and the second author, which considered the case where $R$ is a field.