The Stacks project

Corrections in sets.tex and categories.tex

Thanks to Wouter Zomervrucht

LaTeX: \Ob

	Introduced a macro

	\def\Ob{\mathop{\rm Ob}\nolimits}

	and replaced any occurence of \text{Ob}( with \Ob(. There are
	still some occurences of \text{Ob} but these are sets, not the
	operator that takes the set of objects of a category.

LaTeX: \Mor

	Introduced a macro

	\def\Mor{\mathop{\rm Mor}\nolimits}

	and replaced all the occurences of \text{Mor} with \Mor.

Added new tags

More cleaning up of Algebraic Stacks

	More or less OK proof of the easy direction for going between
	algebraic stacks and presentations. It would be good to add more
	material allowing us to work more easily with fibred
	categories...

Split sections in Algebraic Stacks

	Tried to improve the exposition by splitting into small
	sections. Each section has the potential to grow so this
	hopefully makes a bit more sense in the future.

	The section entitled "Stacks" could simply be removed
	altogether.

Splitting out different notions of representability

	Hopefully this will improve the exposition (everntually).