Pathname :absolute -> :relative

[lynch@aristotle.ils.nwu.edu]

Is there a function which will return relative pathnames for an absolute
one?

After the user chooses a file (from choose-file-dialog), I'd really like to
munge the result so that it is relative to ccl: because I know the whole
system is going to be transported to another computer but the file
structure from ccl: down will remain the same.

I'm gonna hack it for now by string parsing, but is there a clean way to do
this?
"TANSTAAFL" Rich lynch@ils.nwu.edu