Just this morning we updated the Stacks project website (huge thanks to Johan Commelin and Pieter Belmans) so that we can now start adding precise outside references. Since the Stacks project is selfcontained we view these references more as pointers to the literature. Currently we have only four examples of this:

- Yoneda’s lemma
- Nakayam’s lemma
- definition of a birational morphism
- galois cohomology and vanishing of brauer groups

If you click on one of these links and then look in the sidebar you should find a gadget with title “References” which gives you a reference. This sidebar gadget only shows up on the page of the lemma and not on the page for the section which contains the lemma; it also does not show up on the page of lemmas for which we have not yet added references.

The hope is that you, dear reader, will help. While browsing the Stacks project you may come to a lemma for which you know a precise reference. If so, please leave a corresponding comment on the page of the lemma.

The way things are setup we can add these specific references to any lemma, proposition, theorem, remark, example, exercise, situation, equation, or definition. I stress once more that these references should be as precise as possible (i.e., point to an exact result and/or an exact page number if known). If the result in the paper referenced is different, it may be helpful to briefly explain how. Also, it is very useful if multiple references are given for a single result.

More technical information can be found in this post. At the moment parts 1, 2, 4, 5, 6, and 7 of the list there are done. Please feel free to help with parts 3, 8, and 9.

In fact the Yoneda lemma arose in a conversation between Mac Lane and Yoneda in Gare du Nord (see http://www.mta.ca/~cat-dist/catlist/1999/yoneda), but perhaps this is not the sort of information that is needed ðŸ™‚

Nakayam’s Lemma should be Nakayama’s lemma…