[plt-scheme] Y Combinator Exercise

Hi all,

Although some nice things about Scheme are not taught in our
Programming Fundamentals Course I've written some 'harder/research'
exercises to introduce them to some nice concepts which I make
available online during the semester. I've already sone some for
call/cc, the use of very basic operations to define some scheme
implementation code, webpages and I'd like to write something about
the Y Combinator but I'm missing ideas for an exercise where they
could apply the concept of Y Combinator. It should not be too easy but
also not too hard since this should be for them to grasp by themselves
this concept. First I though about giving them an introduction to the
Y combinator and then to ask them to solve the problem of the Towers
of Hanoi for 8 discs for example by writing recursive definitions
using the Y combinator.

But I would like to know if someone has any other suggestion.

Thanks a lot,
--
Paulo Jorge Matos - pocm at sat inesc-id pt
Web: http://sat.inesc-id.pt/~pocm
Computer and Software Engineering
INESC-ID - SAT Group