I appreciate the review and great feedback @gregory.latinier :)

That's a very good point about prettier.

I've opened Issue #18 to add the dependency.

Concerning the mismatched function notation. Early in the project I was having a go at avoiding ES6 on the theory that I could keep my code exceptionally small. That approach fell by the wayside. The line you pointed out was overlooked in switching gears.

I've opened Issue #17 to handle that soon.

Finally — yeah, the ol' school loop =) — by coincidence I had read recently that for is faster than forEach and the size of the set is potentially unlimited. So, I thought it might matter. But I'm not sure yet and I may indeed end up using forEach for readability.

Thanks for the several valid points!