“A JOIN is really a cartesian product (also cross product) with a filter.” It always boils down to this for me.

Not there yet, but yes, people are thinking about this:

https://en.wikipedia.org/wiki/Lithium%E2%80%93air_battery

They might like the book "Super Scratch Programming Adventure!" It walks through building several games in a comic-book format. I thought it was good.

Thanks, that does look good! I'm glad there's a new book out, the other books on Scratch look too dry, too outdated, or both. Ordered a copy.