Just one comment here: This is a masterful summary of many months work pursuing hard-won insights; thank you; let’s do this.
— John P.S. Well, not exactly. You didn’t expect *no* comment from me? :-) It is slightly premature to completely outlaw `x instanceof 42`, because of nulls: You can replace that with `x == 42` only if `x` is `int`. With strings, identity is also a problem; `x instanceof "foo"` does not replace with an `==` expression. In the end, if we outlaw `x instanceof 42` the workaround might be `Objects.equals(x,42)` but that incurs boxing overhead if `x` happens to be a primitive. So, I think the fate of `EXPR instanceof CON_PAT` is up for grabs. That said, I’m fine with leaving it out for starters; it can be added after further thought—or not.
