Need info on aircraft separation

According to FAA regulations, is there any restriction on the
horizontal separation of aircraft?

I was unable to find anything in the FAA regs:

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/MainFrame?OpenFrameSet

Part 91, Section 111 ("Operating near other aircraft") doesn't seem to
answer this.  Part 91, Sections 159 and 179 deal with the vertical
flight deck concept based on compass direction, but doesn't indicate
any required horizontal separation.

The real question I'm trying to get an answer to has to do with
whether there is any required horizontal separation of passenger jets
that are flying at different flight decks.

If anyone knows the answer to this, I would really appreciate your
answer.  Thanks!

-Al B.


--
Al B.

"That's jazz.  Jazz is weird.  Kinda like the same thing that goes on in my head."
- Alex Lifeson's rant during La Villa Strangiato in Rush's "Rock In Rio" concert