Chevalley scheme
# Chevalley scheme

A Chevalley scheme in algebraic geometry was a precursor notion of scheme theory.

Let X be a separated integral noetherian scheme, R its function field. If we denote by $X'$ the set of subrings ${\mathcal {O}}_{x}$ of R, where x runs through X (when $X=\mathrm {Spec} (A)$, we denote $X'$ by $L(A)$), $X'$ verifies the following three properties

* For each $M\in X'$, R is the field of fractions of M.
* There is a finite set of noetherian subrings $A_{i}$ of R so that $X'=\cup _{i}L(A_{i})$ and that, for each pair of indices i,j, the subring $A_{ij}$ of R generated by $A_{i}\cup A_{j}$ is an $A_{i}$-algebra of finite type.
* If $M\subseteq N$ in $X'$ are such that the maximal ideal of M is contained in that of N, then M=N.

Originally, Chevalley also supposed that R was an extension of finite type of a field K and that the $A_{i}$'s were algebras of finite type over a field too (this simplifies the second condition above).

