The post was already fairly long for an explanation and I didn't want to weigh it down further. The type system is described in more detail here: https://austral-lang.org/spec/spec.html#type-universes

Thanks. Actually I read that one too. Several mentions of Region but not really a definition that i could find. Not that it’s a big deal, just curious. I infer some similarity with Rust’a lifetimes but I’m a bit hazy on those

Yes, it's analogous to Rust lifetimes. The term is somewhat older, I think I borrowed it from Cyclone: https://en.wikipedia.org/wiki/Cyclone_(programming_language)