I feel like I'm missing something. Suppose `a` is not Type but rather, say, Bool. Then `x` has kind Bool. That is, x is 'True, 'False, or something exotic. K0 @Bool is then a function that takes anything of type 'True or type 'False and gives you something of type K Bool. What I think Richard is getting at is that there isn't anything of type 'True or type 'False, whether at the term level or the type level. These things only exist when `a` is Type (or TYPE rep for some rep :: RuntimeRep). So it's pretty hard to see what you're trying to do.