Suppose that we really do want to interchange the contents
of the files "dick" and "jane". One way to do it is
to move the contents of "dick" into some temporary file,
then move "jane" onto "dick" (which of course clobbers
the old contents of "dick", but we saved them already),
then finally to move the temporary copy of "dick" to
"jane". There are two files named "dick" and "jane" in this
directory. Interchange their contents, then type "ready".
cmp -s jane Ref && cmp -s dick Ref1