The Stacks project

Move material on fitting ideals ealier

fitting ideal ---> Fitting ideal

Thanks to Kiran Kedaya who writes

There appears to a global spelling issue in the Stacks Project: the
phrase "fitting ideal" appears in lowercase in a great many places, but
it should be "Fitting ideal" because "Fitting" is being used as the
surname of one Hans Fitting. (This is similar to confusion about
"Killing forms" in the theory of Lie algebras, which are named after one
Wilhelm Killing.)

Tags: Added new tags

Revert "Tags: Added new tags"

This reverts commit 515802d4c5e34f6abc8561c7075500b916a686a4.

Reason: We should never add tags to a development branch!

Tags: Added new tags

Finding invariant affine opens

Thanks to Angelo Vistoli for discussions

This somewhat long commit constructs invariant affine opens for
codimension 1 points on a finite groupoid. The method is a bit
convoluted. It is essentially a 2 step process where we first find a
dense open where the groupoid is flat and then we carefully glue on an
affine open of the codimension 1 points along the boundary.

We will apply this to prove that a Noetherian algebraic space is a
scheme away from codimension 2. To prove this one can simplify the
arguments in this commit a bit and we will put in a remark pointing this
out later on.

Finding invariant affine opens

Thanks to Angelo Vistoli for discussions

This somewhat long commit constructs invariant affine opens for
codimension 1 points on a finite groupoid. The method is a bit
convoluted. It is essentially a 2 step process where we first find a
dense open where the groupoid is flat and then we carefully glue on an
affine open of the codimension 1 points along the boundary.

We will apply this to prove that a Noetherian algebraic space is a
scheme away from codimension 2. To prove this one can simplify the
arguments in this commit a bit and we will put in a remark pointing this
out later on.

Finite groupoids

We are going to write a tiny bit more about finite groupoids in order to
prove a result on the existence of invariant affine opens. This is the
first commit.