unique ability A where a : Nat
unique ability B where b : Nat

noGood : Nat ->{A} '{B} ()
noGood n unit =
  -- The A.a should be an ability check failure, since we are in the body
  -- of an arrow which only has the {B} ability set.
  A.a
  B.b
  ()

ok : Nat ->{A} '{B} ()
ok n =
  -- This is okay, because the A.a is being evaluated in the body of an
  -- arrow with {A}. The result of the body is another lambda which
  -- is allowed {B} requests by type signature of `ok`.
  A.a
  'let B.b; ()