2 had me a bit confused at first, but thinking about it from the 'inside out' really helped
3 was easy enough.

I'm starting to understand the structure of subqueries. Each subquery
produces a list or result that acts as a restriction or specification
for its parent query.
INTERSECT was a little annoying to find.

Although, it seems that there would be something more intuitive than
intersecting two whole queries.
I think I'm getting the hang of this.

I've started writing the last subdirectory first, working my way
backwards. It helps to make sense of each query in my head.
Done! If there's another commit after this one...

It means I found a mistake in testing.