Oh, it's easy seeing unique rectangles without greens. One end is always a pair -- that's obvious. And then you just check for someplace where the other end could possibly be. It's not hard. Sometimes one of the other end cells matches your pair cells. That's a type one unique rectangle. Sometimes both the other end have one matching number but not the other. That's a type 2. Sometimes you see a bend or a skew -- rarely -- then you check for a bent or skewed unique rectangle. It's all pretty easy. You don't have to be able to visualize very much at once.