pub fn lift_sum<'a, Row: 'a, F1: 'a, F2: 'a, Lift: 'a>(
    lift: Lift,
    sum: AppSum<'a, Row, F1>
) -> AppSum<'a, Row, F2> where
    F1: TyCon,
    F2: TyCon,
    Row: SumFunctor,
    Lift: NaturalTransformation<'a, F1, F2>,