Since free will is about as easy as a philosophical problem in reductionism can get, while still appearing "impossible" to at least some philosophers, it might make a good training problem for aspiring reductionists. If you consider yourself one of those, consider just reading the free will problem page, and not reading the solution pages below until you've made a serious effort of your own.
Related Pages: Consciousness, Free Will, Philosophy, Reductionism.
(Items in italics can be skipped if in a rush.)