Oh... thank you. My mind is slow today, and, I'm used to the limitation of my 50/34 double, which can't mount a smaller ring (and a triple would have been difficult on my bike). So yeah! Just put a smaller chaining on the Dahon 12! In the video, that looks like a 52 or 53 on a 5x130mm BCD. So for low enough, like a 33 or 34T, that's too small to fit on 130 BCD, you'd need to swap out the crank, I prefer 5x110mm BCD, 50/34 is common, and you could leave on the 50 as a chainguard, or find a chainguard in that size. The only issue there is, that low, the high gear will be 80 inches, that's a bit too low, so I would advocate just a tiny bit wider range on the cassette, if possible.