[plt-scheme] plai: lazyness and exercise 6.4.2

You have at least a partial understanding of what is going on, which
is a start.  However, you haven't stated a concrete question.  What
precisely is the problem you're trying to solve (in your own words),
and how far do you think you've gotten?  Do you think you have a
solution that is correct but too complex, or one that is correct but
only partial, or no solution at all?

Shriram