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> Fair enough, "is assignable to" is another synonym for "is subset of".

Only if you're happy to conflate members and sets, which is pretty confusing IMO. If I write a = b I don't generally think of b as being a set, even though in some sense it is; "b is an expression with this type" is a much more natural way of thinking to me.

> it's quite unintuitve that "never" is assignable to anything

Yeah, at first I was mislead by this.

Initially I thought never is opposite of any while, it turns out, it's opposite of unknown. And any is just super weird, dynamic wildcard thing that is as large or as small as needed for any given operation (but not as small as never).

It's harder for me to make that connection but thank you for your write up. It's really great.

Because "never" is an empty set and empty set is a subset of all sets.

Exactly, that's why I wrote the article =) Makes perfect sense in "set world", but not in "common sense" based on your feeling of the word "never"