Galois Theory and the Existence of Maximal Unramified Subalgebras
Galois Theory and the Existence of Maximal Unramified Subalgebras
Let $B$ be a commutative ring with 1, let $G$ be a finite group of automorphisms of $B$, and let $A$ be the subring of $G$-invariant elements of $B$. There exists a $G$-stable, unramified $A$-subalgebra of $B$ which contains every unramified $A$-subalgebra of $B$.