The Stacks project

Finished cleanup decent-space.tex

	Last edit to this chapter for now.

Decent Algebraic Spaces

	Created a new chapter "Decent Algebraic Spaces" and moved most
	of the material on local conditions of algebraic spaces in
	there. In the next few commits we will fix the breakage that this
	causes.

	The reason for the move is that this material is difficult to
	understand for the beginner and that most of the other material
	in Properties of Spaces and Morphisms of Spaces is easier and
	more analogous to what happens for schemes.

	An added advantage is that we can use results on morphisms of
	algebraic spaces in the new chapter, hence it becomes easier to
	develop the theory of decent spaces.

Decent Algebraic Spaces

	Created a new chapter "Decent Algebraic Spaces" and moved most
	of the material on local conditions of algebraic spaces in
	there. In the next few commits we will fix the breakage that this
	causes.

	The reason for the move is that this material is difficult to
	understand for the beginner and that most of the other material
	in Properties of Spaces and Morphisms of Spaces is easier and
	more analogous to what happens for schemes.

	An added advantage is that we can use results on morphisms of
	algebraic spaces in the new chapter, hence it becomes easier to
	develop the theory of decent spaces.

End conversion of etale to \'etale.

Morphisms of Spaces: Valuative criterion + finite separable extensions

	In the existence part of the valuative criterion for algebraic
	spaces it is enough to take a finite separable extension of the
	fraction field of the dvr. It is sometimes also necessary. It
	seems that if the morphism is separated, then it shouldn't be
	necessary, but we'll return to that later.

Properties of Spaces: Split out arguments on points of spaces

	The purpose of this commit is to work out in more detail the
	arguments that lead to the result that a reasonable algebraic
	space X has a sober space of points |X|.

	In this reworking we discover the notion of an ``almost
	reasonable space''. An algebraic space X is almost reasonable if
	for every affine scheme U and etale morphism U --> X the fibres
	of U --> X are universally bounded.

	Later we will encouter the following question: Suppose given a
	fibre square diagram

		X' --> X
		|      |
		v      V
		V' --> V

	with V' --> V a surjective etale morphism of affine schemes,
	such that X' is reasonable. Is X reasonable? If you know how to
	(dis)prove this then please email stacks.project@gmail.com

	Anyway, the corresponding result for ``almost reasonable''
	spaces is easy. Moreover, an almost reasonable space is a
	colimit of quasi-separated algebraic spaces.

	But on the other hand, we do not know how to prove that an
	almost reasonable space X has an open dense subspace which is a
	scheme, nor do we know how to prove that |X| is sober.

Tags: New tags added and two fixed

Properties of Spaces: Cleanup of results so far

	We added a remark recalling some of the pertinent facts about
	etale morphisms of schemes in the section on points of
	reasonable algebraic spaces. Then we use this to shorten the
	proofs of the lemmas in that section. We added a lemma saying
	that a reasonable algebraic space covered by the spectrum of a
	field is the spectrum of a field. Finally, we changed the lemma
	stating that the topological space associated to a reasonable
	space is sober into stating that it is Kolmogorov. The proof was
	incorrect, and it will require considerably more work to prove
	this.

Properties of Spaces: Reasonable => sober

	It is a little bit rough here and there and some references need
	to be added. Also some of the arguments are duplicated.

Properties of Spaces: Reasonable spaces have sober underlying |X|

	We have not yet completely proved this but it looks like it is
	going to work out. This commit has two FIXMES