The Stacks project

Every algebraic stack has a presentation

	This is the easy direction, although there is plenty to improve
	on here. We should split out some of the discussion in separate
	lemmas. In particular, we should have a discussion on criteria
	which garantee that a morphism of stacks in groupoids is an
	equivalence. We should discuss more generally the construction
	where given
		U ---> X
	with X an algebraic stack, U an algebraic space, on setting R =
	U \times_X U we get a morphism of stacks in groupoids
		[U/R] ---> X
	for free. Then the lemma becomes much more readable and just
	says that if U ---> X is smooth and surjective, then the
	associated 1-morphism is an equivalence.

Tags: added new tags

Groupoid spaces: abstract quotient stacks

	Some formal lemmas on properties of a quotient stack of a
	groupoid space. Coming up: a description of its morphisms,
	objects, etc.