[plt-scheme] Re; define syntax lexical closures

> It's not clear to me why you need special support for part 3.  Why not
> just use Scheme's support for lexical closures?
> <snip>

  Hmm, thanks..  All the stuff they don't teach you (or even hint at) in
the beginning scheme classes.  (I asked R. Dyvig once something to the
effect of whether they're were easier ways to do some things, and he said,
"Yes, but we never show you those..")

Jim