containsVar :: (Ord v, HasVars f v, HTraversable f, HFunctor f)
            => v -> Cxt h f a :=> Bool
containsVar v = unK . free (containsVarAlg v) (const $ K False)
containsVar :: (Ord v, HasVars f v, HTraversable f, HFunctor f)
            => v -> Cxt h f a :=> Bool
containsVar v = unK . free (containsVarAlg v) (const $ K False)
containsVar v = unK . free (containsVarAlg v) (const $ K False)