mapKVars :: Visitable t => (KVar -> Maybe Pred) -> t -> t
mapKVars f = mapKVars' f'
  where
    f' (kv', _) = f kv'
mapKVars :: Visitable t => (KVar -> Maybe Pred) -> t -> t
mapKVars f = mapKVars' f'
  where
    f' (kv', _) = f kv'
mapKVars f = mapKVars' f'
  where
    f' (kv', _) = f kv'