Here is a revised version of the patch, which fixes a typo in a comment
and a poorly chosen "what" tag for allocation.

Also, the definition of factorial in my email had a typo.  It should be:

  (define (factorial n)
    (define (fac n acc)
      (if (<= n 1)
        acc
        (fac (1- n) (* n acc))))
    (fac n 1))

Apologies for the sloppiness,

       Mark