``` unison
use builtin Scope
unique ability Async t g where async : {g} Nat
unique ability Exception where raise : Nat -> x

pure.run : a -> (forall t . '{Async t g} a) ->{Exception, g} a
pure.run a0 a =
  a' : forall s . '{Scope s, Exception, g} a
  a' = 'a0 -- typechecks
  -- make sure this builtin can still be referenced
  Scope.run a'
```

``` ucm

  Loading changes detected in scratch.u.

  I found and typechecked these definitions in scratch.u. If you
  do an `add` or `update`, here's how your codebase would
  change:
  
    ⍟ These new definitions are ok to `add`:
    
      ability Async t g
      ability Exception
      pure.run : a -> (∀ t. '{Async t g} a) ->{g, Exception} a

```