Where in Magento is formed Sql request for the formation of layered navigation?

In the resource model certainly, but I have a vague suspicion that if the answer to this question is sought not in the code and in the forum, then the problem is something else.

And we are talking about the filters say? I mean the filters in layered navigation. I need to make so that the selected attribute is not lost from the filter and remained in the left column and too "filtered". Can't find the file where it can be done.