Since the last update about 3 weeks ago I have added a small amount of material on morphisms of algebraic stacks and some more material on generic flatness and the flattening stratification. I will discuss some thoughts related to this in another post.

Today, I got an email from Christian Kappen mentioning a mistake in Lemma Tag 002X. You can figure out what the mistake was by looking at the development log. It was easy to fix the lemma by adding an extra condition — but it was used in a number of places. It actually took quite a bit of work to repair. Here is the list of lemmas which were affected: 002X, 004X, 002Y, 04B0, 00XS, 04BH, 04BB, 020W, 020Y, 0210, 021E, 021F, 021H, 04HC, 04HD, 021V, 021W, 04CC. I’ve fixed all those places, and hopefully that is it.

One thing I observed while I was doing this is that actually always referencing the exact result that is being used (which is one of the goals of the stacks project) is extremely useful. Namely, you can grep the tex files for the latex label and quickly find all the spots where a given result is being used. Moreover, if every lemma/proposition/theorem states all its assumptions (another goal of the stacks project) then it becomes relatively straightforward to check whether other lemmas/propositions/theorems that are being used in the proof are applicable. Thus such a repair can often be completed in a short time.