Murray, I enjoyed that quite a bit, but it's really strumming that gave me special trouble, and I'm looking into. But the thumbnail thing is similar to what I'm doing--it's almost a sweep arpeggio down-up with the thumb while a finger, usually my middle does a down with the thumb-downstroke, then up slightly off-synch with the thumb up. I almost can't tell what I'm doing anymore but it rolls very easy and fast, sounds crazy on a mandolin. I'm thinking I've heard something like it in flamenco stuff, I don't know.