Date: Thu, 11 Jun 81 03:23:00 -0400 (EDT)
From: Dan Hoey <Hoey@CMU-10A>
To: Cube Lovers
Subject: Re: edge "flip" anyone...

  Does anyone know of a way to flip two edges without changing
  anything else, ie interchange the FR and FB edges, keeping their
  same orientation.

The term "flip" generally means "change orientation" (of an edge).  I
take it you mean "exchange" (or, acceptably, "interchange").  This is
provably not possible, because an exchange is an odd permutation.  I
will send you the two messages which deal with what can be done with a
cube.  (Anyone else who wants a copy, request of Hoey@CMU-10A rather
than the list.)

If you don't know what an even (or odd) permutation is, or how it
acts, any elementary algebra text should help.  If you try and fail,
drop me a line and I'll try to help.

  If not, how about one that will interchange FR and FB edges without
  disturbing the top layer, but can mess up the bottom??

There is no FB edge.  I'd guess you mean UR and UB, for which RU'R'
UUFFBB DDFFBB RUR' suffices.