For those who haven't read SICP: don't get the impression that it only deals with very easy stuff like the example in the post about turning a recursive definit

For those who haven't read SICP: don't get the impression that it only deals with very easy stuff like the example in the post about turning a recursive definition into an iterative one. It actually touches on many of the bet ideas in CS. This post could have easily chosen a more interesting example.