I like like the small stuff. Iterative things. Feedback loops.
Take a basic set of r...ules and run something through it - a
number, a grammar - whatever it is.. Take what you get and run
it through again, and again. Or run it through a second machine
and then feed it back until you get a particular 'something'
that you're looking for, then move on to the next set of simple
steps. "