parallel and sequential binding.

[RMS at MIT-AI (Richard M. Stallman)]

How about changing PROG to bind its variables in parallel
like DO and LET, but introducing PROG* which would bind them
sequentially as PROG does now.  PROG* would be like LET*.
Then there could also be DO*.  This would result in more functions
with more choices, but the whole lot would be easier to keep straight
than the set which we have now.
To convert, we just have to change PROG's to PROG*'s in existing code
when they look like they might possibly depend on the order of binding.