[taos-glug] has anybody tried Exercise 1.9?

I've been working on it.   I understand, I think, how the two
programs work.   But I don't know if the authors have given us enough
information to answer their question definitively.  The "substitution"
model is not really very well explained, IMHO.

And iterative or recursive?   Do they mean syntatically recursive or "truly"
recursive?

Maybe there is no definite answer.  Maybe it's a "discussion" question.

Or, maybe the best answer is a counter-question:  What difference does it
make? The programs are, after all, rather artificial.

To avoid getting stuck, I decided I'd have to get rough with it.   I "cheated."
I used the "begin" statement (or "special form," I guess).   It has not been
introduced in SICP prior to exercise 1.9.

But, using it, I was able to put "display" statements at critical points
to help me analyze the process.

How did other people approach this exercise?

Philip

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