[plt-scheme] Outer-inner loops in Scheme?

I 2nd Will's use of comprehensions.

Additionally note that often looping over integers is a distraction.
Often you want to loop over every element, or even every index (if
you're using an array), but it is quite rare that one just wants to
loop over an arbitrary subset of integers.  You can make your code
clearer and less error-prone by making these concepts explicit in your
code.

N.