Right, comments. Just a little important, aren't they? :P
You raise a good point... it's the same number of parentheses either way. But in that case, why not just have let and lets (as given(s)), and be done with it?
Edit: as an aside, given that pg has said that he'll modify Arc as if there's nobody else programming in it, and that he does not appear to be using Anarki, eventually when Arc3 does come around, it is very possible that Anarki will be incompatible with Arc3. We may very well need to build a converter program in the future to transform Arc2-base Anarki to Arc3-base Anarki, so my abstract nonsense may very well be necessary in the future.