[nukifw]

Yes, the trick is expanded here: https://libres.uncg.edu/ir/asu/f/Johann_Patricia_2008_Founda... (if you have `Eq a b = Refl : a a eq` you should be able to encode every useful GADTs. But having a compiler support is nice for specifics reason like being able to "try" to detect unreachable cases in match branches for examples.