I am not quite sure that this question is appropriate for Mathoverflow, yet I would be deeply grateful for any hint: what happens in section 3 of Beilinson A., Bernstein J., Deligne P., Faisceaux pervers//Asterisque 100, 1982, 5-171? Is there any statement that is important for the following sections of this treatise? I do not know French; yet this does not prevent me from understanding all the other sections.


Upd. I wonder: does there exist a 'plan' of BBD?



What is the purpose of section 3 of BBD?
I'm not an expert at BBD, but the introduction explains that chapter 3 is supplementary technical information that can be skipped. For example, if you want to work with $\mathbb{Z}$-coefficients, or the filtered derived category, you might find chapter 3 useful. As far as a "plan" of BBD is concerned, the introduction has a brief description of the contents of each chapter, but if you are looking for some kind of "tree" of lemmata leading to main results like the decomposition theorem, I haven't seen one.


I only found 3 references to chapter 3 in the rest of the book:


1. The proof of Proposition 2.1.23 uses section 3.2.
2. Part 2.2.19 gives a proof of Proposition 2.1.23 that does not use results of chapter 3.
3. The first page of chapter 4 mentions section 3.3 in an inessential way.


